Use string for Node version in .travis.yml

0.10 as a float == 0.1, the version should be a string.

Fixes the [Travis build](https://travis-ci.org/google/traceur-compiler).
Change the AST for ImportSpecifier and ModuleDeclaration to contain
a ImportedBinding tree.

Fixes #1154
Add support for the exponentiation operator

x ** y is now short for Math.pow(x, y)

Similar for x **= y.

https://gist.github.com/rwaldron/ebe0f4d2d267370be882
Add support for "import * as m from 'm'"

This keeps the old syntx in place. It will be removed in a seperate
PR since self hosting requires this two step process.

Partial fix for #1119
0.0.54
Commit binaries for 0.0.54