Make line indices configurable

[dabbler0]

Allow the user to configure whether line indices are zero-based or one-based, like SpiderMonkey's Reflect.parse.

[RReverser]

IMO it's pretty hard to standardize such things (de-facto they became so with Source Maps location format), and would be even harder if we start provide options for 0- or 1-based lines or columns on parser and tools levels. Also, I'm not sure if it's worth to include such simple yet rarely needed functionality on parser level since subtracting/adding of 1 is pretty simple operation to be done in any Acorn API consumer. Thoughts?

[marijnh]

I agree with @RReverser here. Rather than trying to handle this option properly throughout Tern's sources, client code will just have to adapt the coordinates it gets from Tern into its own system.