Compiler Cleanup and Documentation

[water111]

Add documentation and do a lot of little cleanup things in the compiler. There's still some stuff to clean up after this but I want to save that until refactoring the Register vs emitter::Register and settable stuff.

[coveralls]

Pull Request Test Coverage Report for Build 271329032

• 185 of 211 (87.68%) changed or added relevant lines in 17 files are covered.
• 19 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.3%) to 64.16%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
goalc/compiler/CompilerSettings.cpp	4	5	80.0%
goalc/compiler/compilation/Atoms.cpp	14	15	93.33%
goalc/compiler/compilation/Block.cpp	10	11	90.91%
goalc/compiler/Val.cpp	0	2	0.0%
goalc/compiler/Val.h	1	3	33.33%
common/type_system/TypeSystem.cpp	7	10	70.0%
goalc/compiler/compilation/CompilerControl.cpp	1	8	12.5%
goalc/compiler/compilation/Function.cpp	29	38	76.32%

Files with Coverage Reduction	New Missed Lines	%
goalc/compiler/compilation/Function.cpp	1	85.94%
goalc/regalloc/Allocator.cpp	5	79.63%
goalc/compiler/compilation/CompilerControl.cpp	6	53.19%
goalc/compiler/Val.h	7	52.24%

Totals
Change from base Build 262974948:	0.3%
Covered Lines:	14094
Relevant Lines:	21967

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💛 - Coveralls