wavbreaker 0.13

A new version of wavbreaker is out with some build system fixes and with a CPU-hogging fix for Moodbar generation:

• Improve support for older compiler versions (patch by Jan Beich, #6)
• Fix a crashing bug related to multi-threading and UI rendering (Fixes #7)
• Add snapcraft.yaml
• Fix CPU usage during Moodbar generation
• Build Flatpak package in releases