MapRoller 0.3.0

This update doesn't include any new features, but it does completely rework the save system so project files and presets made with previous versions will no longer work.

The new save system uses JSON files instead of the arbitrarily-defined plaintext format I was using before. It also fixes a bug that causes dice in dice sets to duplicate when loading certain maps. Additionally, most updates will no longer break saves from previous versions.