0.6.3

- Fix compilation warnings
- autoconf: Some updates
- Update `.gitignore`
- Remove GSourceFunc casts
- Fix missing-prototypes
- Bump required GLib version to 2.56
- Implement ISO 8601 time format to avoid post-2.56 GLib functions
- settings: Drop subtitle
- Fix multiple memory issues (!11)
- Translation Updates:
  Albanian, Arabic, Armenian (Armenia), Basque, Belarusian, Bulgarian,
  Catalan, Chinese (China), Chinese (Taiwan), Croatian, Czech, Danish,
  Dutch, Eastern Armenian, English (Australia), Estonian, Finnish,
  French, Galician, Georgian, German, Greek, Hebrew, Hungarian,
  Icelandic, Indonesian, Interlingue, Italian, Japanese, Kazakh,
  Korean, Lithuanian, Malay, Norwegian Bokmål, Polish, Portuguese,
  Portuguese (Brazil), Russian, Serbian, Slovak, Slovenian, Spanish,
  Swedish, Thai, Turkish, Ukrainian
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