- Renamed "OsuFile" to "Beatmap". All related variables and methods with "osu" have also been renamed to "beatmap" (or variants of each).
- Renamed "OsuGroupNode" to "BeatmapSetNode". Avoids confusion since groups are identified by a "set ID", not a "group ID".
- Renamed "OsuGroupList" to "BeatmapSetList", for the same reason as above.
- Renamed "OsuDB" to "BeatmapDB", for the same reason as above.
- Moved classes directly related to parsed beatmaps (Beatmap, BeatmapSetList, BeatmapSetNode, OsuHitObject, and TimingPoint) into a new "beatmap" package.
Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>
