2.0.0

Desktop integration, marking the start of a new direction.

Now that the main gameplay for the standard mode is there, it's time to make it
easier to use for everyone. 2.0 features an experimental beatmap indexer
generating an HTML listing of all your beatmaps. Coupled with the desktop
integrations, you can open oshu! from your web browser.

The codebase was migrated to C++ to benefit from stronger type safety and
automatic memory management. The build system is now CMake instead of the
autotools, preparing for Windows support.

With CMake, no need for specific distribution tarballs, you can use GitHub's automatically generated tar.gz, or download the release from https://www.mg0.fr/oshu/releases/oshu-2.0.0.tar.gz