add comprehensive generation tests
fix up let scoping transformer comments
support async functions in generator and move MethodDefinition to class generator
generator: correctly output XJSEmptyExpression
make it illegal to use destructuring outside of an ExpressionStatement
allow XJSElement and SequenceExpression to be user whitespacable
add single spread test
remove unneccesary Literal generator raw
fix up semicolons for module ExportDeclaration generator
fix WithStatement missing paranthesis
optimise types.toStatement for when we're directly passed a statement
add toIdentifier, toBlock and toStatement tests
fix newline in let-scoping/for-break-continue-return test