EAGLESIX-2687 updated port of Value
docs from another pass thru the 2.6.5 value files

This one is pretty important so I wanted to make another pass through and capture any docs that I could glean from the original `value.cpp` and `value.h` files (and reorder things similarly to how they have them to make bug fixing easier).
Merge branch 'feature/mongo_2.6.5_expressions' into feature/mongo_2.6.5_expressions_Value

Conflicts:
	lib/pipeline/Value.js
EAGLESIX-2687: mv Value test file into tests dir
EAGLESIX-2651: Value: stub tests; mv _coerceToNumber to coerceToNumber and add docs for this minor deviation
EAGLESIX-2651: Value: add tests; fix issues found
Merge pull request #4 from RiveraGroup/feature/mongo_2.6.5_expressions_Value

Feature/mongo 2.6.5 expressions Value