Implement ES2016 check for simple parameter list in strict mode (#106)

* 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.

test/fixtures/es2016/simple-parameter-list/generator-function/actual.js

@@ -0,0 +1,3 @@
+function* a(options = {}) {
+  "use strict";
+}

test/fixtures/es2016/simple-parameter-list/generator-function/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Non-simple parameter in strict mode (1:12)"
+}