0.0.44
Remove ErrorReporter use in InternalLoader. Throw from LoaderHooks.

(Next step will use promises for communicating errors from LoaderHooks)
Remove unused ErrorReporter in ModuleSpecifierVisitor

Review URL: https://github.com/google/traceur-compiler/pull/1052

Closes #1052.
Fix hoisting of let/const declarations.

Only hoist top-level let/const declarations and fix bug with
initializers of hoisted declarations.

Fixes #1028.
merge