Fix `String.prototype` polyfills

Ref. #562.
Rename RequireJs and NodeJs transformers and options

The options are now cjs and amd.

The transformers are now AmdTransformer and CjsModuleTransformer.

Fixes #547
Replace Project with Loader in repl.html

Adds InterceptOutputLoaderHooks module for grabbing transcoded source and map.
Changes Loader.evalAsync() to Loader.module(source, options) closer to spec.
Adds name to Loader.eval() calls, as proposed in https://github.com/jorendorff/js-loaders/issues/82.

Review URL: https://github.com/google/traceur-compiler/pull/564

Closes #564.
Remove assertThrows and use assert.throw instead
Fix error in parsing Arguments

Make sure we do not allow trailing commas in arguments.

Fixes #570
WebLoader.load -> webLoader.load; similarly nodeLoader and fileLoader.

The load methods do not use 'this' and can be simply functions.

Review URL: https://github.com/google/traceur-compiler/pull/575

Closes #575.
Replace WebPageProject in runner.html with new WebPageTranscoder

Loader based testing rather than Project based.

Review URL: https://github.com/google/traceur-compiler/pull/573

Closes #573.
Add test for static methods in export/import

Works for me

Review URL: https://github.com/google/traceur-compiler/pull/574

Closes #574.
Increment npm version