Remove some more cruft for legacy browsers.

https://code.google.com/p/esprima/issues/detail?id=474
Code coverage: ignore known uncovered branches and statements.

https://code.google.com/p/esprima/issues/detail?id=518
Stub to document ES6 official support.

https://code.google.com/p/esprima/issues/detail?id=499
Remove stacked markers.

https://code.google.com/p/esprima/issues/detail?id=520
Simplify markers; Remove location marker.

https://code.google.com/p/esprima/issues/detail?id=520
Avoid small range object in working tokens.

https://code.google.com/p/esprima/issues/detail?id=520
Fix Traceur on the speed comparison page.

https://code.google.com/p/esprima/issues/detail?id=424
Simplify regular expression scanning.

To reduce the complexity, split it into body and flags scanning.
Also, as suggested by Bei Zhang, separate the testing of regular
expression so that it's try catch won't reduce V8 performance.

https://code.google.com/p/esprima/issues/detail?id=396