Release v1.17.0 (for Beat Saber v1.17.0)

See the README file for installation and usage instructions.

Changes:

• Support for Beat Saber v1.17.0 (#73, by @ErisApps)
• beatmap.difficulty now represents the name of the difficulty in the game's current language. If SongCore is installed, this value may contain the custom difficulty name defined by the beatmap, however I've not actually seen that happen. (#70)
• The mod now targets .NET v4.7.2

Adds:

• beatmap.difficultyEnum representing the internal beatmap difficulty enum. See protocol.md for more information.

Fixes:

• Exception thrown when SongCore is not installed while extracting value for beatmap.songHash. (#69, by @rynan4818)