This commit enables optional features that are enabled by default in the generated parser.
For now, only some of the helpers and filename are generated based on this new option, but this will change in the future most likely.
Resolves#421
Before there used to be some internal utility methods for arrays and objects, but as the code base moved to ES5+ use case only, these were removed in favour of native alternatives, but most of these were only beneficial for arrays.
This commit add's common utility methods for objects, and also exposes these as they can be used by plugin developer's on the PEG.js AST.
* Optimization: do not generate unreachable calls |peg$fail| and constants for it (local to the rule).
* Optimization: do not generate unreachable calls |peg$fail| and constants for it (non-local to rule).