Ambience, Achievements, and Mineclone2 support

This release has a lot of changes under the hood to allow cross-compatibility with Mineclone 2. Mineclone 5 support is pending a pull request to that game's repository.

In addition, several new features have been added. Most significantly: there are ambient sounds that play in the various subterranean caverns that correspond to the biomes they contain, and a set of achievements have been added based on the "awards" mod.