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.