This is a tiny change that fixes a currently unimportant memory leak
in main.cc.

This simplifies updates over time (that is: users who are using default
values will automatically receive the updated values when switching
from xfce4-sensors-plugin version N to version N+1).

Changes:

- Remove sensors_init_default_values() -> Add t_sensors constructor
- Specify default values in 1 place (t_sensors constructor),
  instead of 2 places (sensors-interface-common.cc, configuration.cc)
- Add xfce4::Rc::write_default_... functions
- Add support for floating-point values (32-bit) to xfce4::Rc
- Add parse_float() and parse_double()

Fixed issues:

- Save the current width&height values (not the stale values) to RC file
- Rc::read_entry() fallback code-path

See also: #26

The updated behavior takes effect only when a new instance of this plugin
is added to a panel. Configurations of existing instances are not fixed by
this patch because the RC configuration file already/always contains the
Show_Title item irrespective of its default value.

Closes: #26

List of changes:

- t_labelledlevelbar *panels[MAX_NUM_CHIPS][MAX_NUM_FEATURES] -> std::map
- GtkTreeStore *myListStore[MAX_NUM_CHIPS] -> std::vector
- Remove the constants MAX_NUM_CHIPS and MAX_NUM_FEATURES
- t_sensors* -> Ptr<t_sensors>
- t_sensors_dialog* -> Ptr<t_sensors_dialog>
- Move NULL pointer checks from run-time to compile-time
- Remove redundant @param in the documentation of functions
- Add xfce4::put(), because std::map.insert_or_assign() is a C++17 feature

As a side-effect, this avoids the invalid documentation "returns >0 on
error" when the function was actually returning negative integers in case
of an error.

The type-safe GTK wrapper functions (new file gtk.cc) have been copied
from the most recent version of xfce4-cpugraph-plugin, and several new
type-safe wrappers have been added as required by xfce4-sensors-plugin.

The conversion from a less safe C code to a more safe C++ code revealed
several issues that were missed because of the simplicity of C's type
system. Slider value handlers in the UI-style panel (in the properties
dialog when tachos are selected) were returning void, instead of gboolean,
which means that the sliders were being updated according to the
pseudo-random value present (in case of an AMD64 binary) in the %rax
register when the handler function returned to its caller (the caller
was expecting a non-random gboolean in the %rax register).

Configuration dialog changes:

- Align elements in the UI-style panel when configuring tachos

See also: https://gitlab.xfce.org/panel-plugins/xfce4-cpugraph-plugin/-/tree/5a33de908bbed4c71648...

Please note that the code hasn't been thoroughly examined/tested for
memory leaks yet.

Changes:

 - gboolean -> bool
 - gchar* -> std::string
 - gpointer chip -> Ptr<t_chip>
 - gpointer chip_feature -> Ptr<t_chipfeature>
 - GPtrArray -> std::vector
 - t_chip* -> Ptr<t_chip>
 - Remove @param comments describing just the parameter's data type
 - GtkWidget *tachos[MAX_NUM_CHIPS][MAX_NUM_FEATURES] -> std::map
 - Remove hard-coded limit on the maximum number of tachos
 - Remove redundant field t_chip::num_features
 - free_chip() -> t_chip::~t_chip()
 - free_chipfeature() -> default auto-generated destructor
 - new t_chip() -> xfce4::make<t_chip>()
 - new t_chipfeature() -> xfce4::make<t_chipfeature>()

Bug fixes:

 - strncmp(disk, "/dev/fd", 6) -> xfce4::starts_with(disk, "/dev/fd")

For example, xfce_rc_read_X(rc, args...) has been replaced with
rc->read_X(args...).

xfce4++::Ptr and xfce4::Rc have been copied from the most recent version
of xfce4-cpugraph-plugin.

This patch also fixes an invalid chip->sensorId comparison introduced in a
previous code cleanup.

See also: https://gitlab.xfce.org/panel-plugins/xfce4-cpugraph-plugin/-/tree/9b594c5b7c1e11612e0aab2a5a78125b308f6ed4/xfce4%2B%2B/util

Xfce4++ string utilities have been copied from xfce4-cpugraph-plugin,
without modifications. About 80 lines of code have been removed from
xfce4-sensors-plugin as a consequence of using std::string, new and
delete (not counting lines added in the xfce4++ directory).

See also: https://gitlab.xfce.org/panel-plugins/xfce4-cpugraph-plugin/-/tree/ef5acc3b38b0954965f21f5193807404b9e50a45/xfce4%2B%2B

This adds parameter types to ELF symbols representing functions, which
slightly increases run-time type safety.

Please read the documentation in build-combinations.sh for further info.

The script successfully completes without errors in Linux with
clang 12.0 and gcc 11.2 C/C++ compilers. Other operating systems and
compilers have not been tested.

This saves about 200 lines of code.

The new file plugin.c, comprising of a single line of code, is required
because XFCE_PANEL_PLUGIN_REGISTER is incompatible with C++.

This patch also corrects inconsistent indentation in Makefile.am.

Closes: #16

MR !43

The main purpose of this patch is to replace main.c with main.cc.

This step requires some #include directives of libxfce4util to be enclosed
in extern "C" {} because some of the included Xfce4 C files are missing
G_BEGIN_DECLS/G_END_DECLS macros. This issue has been fixed in
libxfce4util's main GitLab repository, but (1) there hasn't been a release
containing this fix and (2) it would delay xfce4-sensors adoption in
conservative Linux distributions which are upgrading to newer Xfce
library releases less often.

All C++ implementation files (.cc file extension) should include fixes.h
before including any other header files.

See also: xfce/libxfce4util!19
See also: !39 (comment 36108)

This patch also fixes a potentially leaking file descriptor in error
code-paths.

Closes: #24

Most of the configure.ac.in updates were suggested by autoupdate-2.71.

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).

86 translated messages, 1 untranslated message.

Transifex (https://www.transifex.com/xfce/public/).

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).

85 translated messages, 2 untranslated messages.

Transifex (https://www.transifex.com/xfce/public/).

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).

85 translated messages, 2 untranslated messages.

Transifex (https://www.transifex.com/xfce/public/).

Found by: scan-build

Found by: scan-build

Found by: scan-build

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).

87 translated messages.

Transifex (https://www.transifex.com/xfce/public/).