Utilize gc() for V8 and SpiderMonkey

https://code.google.com/p/esprima/issues/detail?id=529
Fix coding styles in test/benchmarks.js.

https://code.google.com/p/esprima/issues/detail?id=529
Remove duplicate markEnd

https://code.google.com/p/esprima/issues/detail?id=528
DRY and generally reduce code in scanPunctuator function.

Performance impact is negligible.

https://code.google.com/p/esprima/issues/detail?id=370
Add a minimal documentation on the tokenizer API.

https://code.google.com/p/esprima/issues/detail?id=398
Fast path in advance() should check for semicolon instead of colon.

https://code.google.com/p/esprima/issues/detail?id=534
Revert "Fix escaped identifier being treated as a keyword."

https://code.google.com/p/esprima/issues/detail?id=496