Fix issue with scanning regular expressions

Since both / and /= are tokens that may start the regular expression we need to go back one or two characters respectively.

This is based on #327 by @seanmiddleditch

Fixes #326
Fixes #327

Review URL: https://github.com/google/traceur-compiler/issues/328

Closes #328, closes #326, closes #327.
Fix issue with generators and empty for loop headers

In case we have neither initializer state nor condition state, set the start state to the start state of the loop body.

Fixes #331

Review URL: https://github.com/google/traceur-compiler/issues/332

Closes #332, closes #331.
Generate tables for ID_Start and ID_Continue and use that in the scanner

Fixes #321

Review URL: https://github.com/google/traceur-compiler/pull/329

Closes #329, closes #321.