Option to compile to AMD

[bregenspan]

Similar to #30, it would be very nice for AMD users to have the option to compile modules to AMD so that a project's own dependency management system of choice can be used. (Where I work, we currently add an AMD wrapper around all Closure Templates-generated JS, but still have to manually ensure that any inner templates that get called are manually added as dependencies of the caller).

Someone submitted a patch for this awhile back in https://code.google.com/p/closure-templates/issues/detail?id=29& , but I've had trouble tracking the author down to see if they'd want to resubmit this now that project is on GH.

[bregenspan]

(In light of #30, one option could be to just compile to some single standard module format like ES6 modules, allowing for a separate module conversion step using preexisting converters for anyone who wants to use AMD, CommonJS, etc.)

[bregenspan]

I'm closing this out because #30 would solve the same problem nicely and work with current common build tools.