Partial (and non-functional) implementation of FlexibleValue.
Working version of scaled asteroid properties.
Merge branch 'master' into relative-values
Documented config commands, added test cases.

Added support for Offset() command

Bugfix: a corrupted or invalid config for one ASTEROIDGROUP will no longer prevent others from loading. This makes Custom Asteroids' behavior the same for load-time and generate-time errors.
Made asteroid labeling on by default. Cleaned up documentation.
Merge branch 'master' into relative-values

Conflicts:
	CHANGELOG.md
	src/Population.cs
Tweaked asteroid spawn rates. Fixed documentation formatting.