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
WIP on String.prototype[@@iterator]; Github issue #539
Use maybeAddIterator
Insert repl options at top of file based on user's choices.

Also rely less on global options.
Fixes #1213.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1219

Closes #1219, closes #1213.
Array.from polyfill: Only use Function#call when thisArg is provided.

This was much slower than it needs to be for the common case, when `thisArg` isn't provided.
Switch to use import * as for code

This removes the support for the old syntax

Fixes #1119
0.0.55
Report options errors in REPL UI

Fixes #1229

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1230

Closes #1230, closes #1229.
Repl: Fix issue where location  was not updated.

This was a regression from 75ca1e0b25027bb152b96245a899bd7d4b57178a

Fixes #1234
Make sure async-functions work without generators.

This was due to a typo.

Fixes #1231
0.0.56
Simplify parsing of for loops

This also enforces that for-in does not have an initializer.
implement Array.of
remove source root for filename

Currently, this implementation is causing the path to double up - `some/file/url.js` becomes `some/file/url.js/some/file/url.js`.

The source root is optional, and only necessary if there are a number of source files that would benefit from having a common root.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1226

Closes #1226.
WIP