Add debug target to build sourcemap

Review URL: https://github.com/google/traceur-compiler/pull/467

Closes #467.
Fix conflict issue with alpha renaming of this in arrow functions

By doing the alpha renaming in the outer function first we do the renaming of inner arrow functions too.

Fixes #466

Review URL: https://github.com/google/traceur-compiler/pull/468

Closes #468, closes #466.
Close GH-472: Refactor ProgramTransformer into FromOptionsTransformer and ProjectTrans....
Unify transformer constructor type signature

This allows us to remove a bunch of boilerplate code.

Review URL: https://github.com/google/traceur-compiler/pull/473

Closes #473.
Fix parsing of arrow functions

Arrow functions should be parsed as AssignmentExpression, meaning that they have the lowest precedence of them all.

Review URL: https://github.com/google/traceur-compiler/pull/464

Closes #464.