chore($parse): convert parser() and lex() to prototype-based code

This reduces memory consumption of parsed angular expressions and
speeds up parsing.

This JSPerf case demonstrates the performance boost:
http://jsperf.com/closure-vs-prototype-ngparser

Chrome: 1.5–2x boost
FF: slightly slower (I would love to know why)
IE: 4x boost

To be clear, this doesn't have any impact on runtime performance
of expressions as demostrated in this JSPerf:
http://jsperf.com/angular-parser-changes

Closes angular#3681