Closes#572
Introduce tests for new semantics for ES2015 features such as
lexically-scoped bindings. Also add tests for semantics defined in prior
editions of the specification but not yet covered in this test suite.
Limit tests in `language/expressions/call/` and `built-ins/eval/` to
only assert details that are directly related to the invocation pattern.
Re-organize all other tests within the `language/eval-code/` directory,
further categorizing each as `direct` or `indirect` as appropriate.
Remove the extraneous "executable" flag from those files which carried
it.
Mike Pennisi