AMD and ES6 interop support

Under modules=amd, mark modules with property '__esModule', and treat all other modules as default exports to allow mixing ES6 and AMD modules under both ES6 and AMD loaders.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/785

Closes #785.
Followup cleanup from last commit
Print a stack trace when the interpreter sees an exception.

Set the process.exit code to 8 on error
Fixes #812

Reviewed on #814.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/823

Closes #823, closes #812.
Simplify the ErrorReporter to not support rest params

The usage of rest params is less useful now that we have full support for template literals.

Review URL: https://github.com/google/traceur-compiler/pull/821

Closes #821
Merge branch 'master' into hoist-variables

Conflicts:
	bin/traceur.js