Add support for goog.module based imports

- option to enable goog modules
- golden file based tests
- based on moduleName for the current file

Based on @vojtajina's initial work.
Conceptually the `Compiler` is -- or can be -- set up once and reused by calling `compile()`. Since this goofy `moduleName` option can be a module-specific string, passing this module specific data on the Compiler could be trouble.  Moving the `moduleName` processing into `Compiler.transform()` would solve this. Plus it's available on `this.options_`.