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.
Include README in npm package
Log value of a superClass when it's invalid

Specially useful as a better error message when the superClass is undefined

In docs, rename UniqueIdGenerator to UniqueIdentifierGenerator
Use template literals when logging an invalid superClass
Add to and export PlaceholderParser

- Makes the error reporting of PlaceholderParser more informative.
- Adds parseModule and parseScript template tags.
- Exports parseModule, parseScript, parseExpression, and parseStatement from
  the main Traceur module, as properties of the codegeneration export.
ensure traceur System is exported not the global
Exponentiation expression should be right associative

Fixes #1245
Destructuring does not require an object any more
0.0.57
Remove runtime remove assertObject

This could not be included in the last commit due to self hostin
issues. It required a npm push before it was safe to remove.
Correct sourceMaps option in test and verify it.

Partly fixes #1254

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1258

Closes #1258, closes #1254.
Hoist function declarations in generator functions

This is so that we do not add a function where it isn't allowed
in ES5 strict mode, due to the CPS transformer.

Fixes #1172
Add support for export default FunctionExpression

and export default ClassExpression

We parse the expression as a FunctionExpression and if it has a name
we change it into a FunctionDeclaration. Same goes for ClassExpression.

Fixes #1208
Define what polyfills to include in the Makefile

The Makefile now lists the polyfills to include. These files register
themselves and then the polyfills.js initializes the polyfills for The
given global.

Fixes #1244
expose traceur.get
Add Options.diff and refactor test to use it

Set Options through setOptions to check for unknown options.
Correct sourceMap -> sourceMaps
Fixes #1254

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1259

Closes #1259, closes #1254.
Support CommonJS loading from ES6

Fixes #818
Tag git with traceur's npm version

rather than the version on bin/traceur.js
Update the version (and publish to npm)
one time without a tag to get in sync.

Fixes #1261

TBR=@arv

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1263

Closes #1263, closes #1261.