Compile kangax's es6 tests and verify the compat-table entries.

The compat-table data-es6.js file builds the web page showing compatiblity results.
Reading that file and extracting the tests allows tracuer results to be verified.
Also, while I'm thinking about API. Why is it called stringToTree when:

1. It does not take a string, it takes a `{content: string}`
2. It does not return a tree, it returns a `{tree: ParseTree}`