Add batch conversion function and GUI

Adds a GUI for batch converting a directory

What's Changed

• Add generated unit tests by @odejesush in #5
• Add integration tests by @odejesush in #6
• Add unit tests for SourceNote, ArrangementContext, and NoteBuilder by @odejesush in #7
• Return title and artist from ConvertAsync by @odejesush in #8
• Support directory input for batch conversion by @odejesush in #9
• Add tests for batch directory processing by @odejesush in #10
• Feature/gui scaffold by @odejesush in #11
• Feature/gui main window by @odejesush in #12
• Build and publish GUI in CI and release by @odejesush in #13
• Document batch mode and GUI usage by @odejesush in #14
• Feature/batch metadata check by @odejesush in #15

Full Changelog: v0.1.2...v0.1.3

v0.1.2

Create macOS assets

v0.1.1

Produce Windows assets