Literal eliding

Features

• Where an expression has an operator that will only ever work on literals, the library will now elide the operator and optimize the literals into a single stage ( #35 ) instead of doing so upon every call to Evaluate() (involves bugfixes on this feature from #46 and #47 )

Bugs

• Fixed a bug where expression parsing would panic if they started with ) (found with #47)
• Fixed a bug where evaluation would panic if parameters contained incomparable types and the expression tried to compare them (found with #47)
• Fixed a bug where parsing would try to optimize tokens before checking grammar, leading to panics with regex operators being used as EOF (found with #47).