Switch Esprima to report index-based ranges.

This will result in a lot less JSON being generated which in turn
cuts the JSON generating/parsing time considerably.

Also, the comments output of esprima only reports index-based ranges
anyway, so we're pretty much bound to use it.

Again, parsing all sencha touch src files:

JsParser:      3.5s
EsprimaParser: 4.0s

That's not much of a performance hit any more.