v0.21

This release contains the following changes:

• Add Basque translation by @aldatsa.
• Make the shuffle and loop command line options work properly.
• Make the main menu button toggleable by pressing F10.
• Add a setting for always appending opened files to the playlist.
• Allow appending files to playlist by holding shift while dropping files onto the video area.
• Make CSD header bar toggleable via the mpv property "border".
• Include Flatpak manifest in the repo. This allows Celluloid to be built in one click in apps like GNOME Builder.

This listing is incomplete. See git log for complete changelog.