Add parseStatements to PlaceholderParser

And use that in the CPS transformers.

Fixes #523

Review URL: https://github.com/google/traceur-compiler/pull/536

Closes #536, closes #523.
Convert CodeLoader() to more closely follow ES6 Loader()

Isolate reporter and project in InternalCompiler.
Rename ModuleRequireVisitor -> ModuleSpecifierVisitor

Review URL: https://github.com/google/traceur-compiler/pull/540

Closes #540.