* Slightly simplify logic
* Implement ES2016 check for simple parameter list in strict mode
See e.g. ECMA-262 7.0 14.1.2:
> It is a Syntax Error if ContainsUseStrict of FunctionBody is true and
> IsSimpleParameterList of FormalParameters is false.
Similar clauses cover arrow functions, generator functions, methods, and
generator methods, as well as async functions and async arrow functions.
* This removes the exponentiationOperator as it is now in es2016
* Remove from tests
* Remove asyncFunctions and restructure test dirs
* Remove trailingFunctionCommas
