Separate Source Code Line Mappings in Skulpt

[acbart]

This is really actually more of a Skulpt thing, but I wonder if it's not a solution for trimming down the code base size significantly for JS-compiled Pedal?

The idea started for #94, where I would have to support out-sourcing large strings to a JSON file anyway. Well, what if we did the same thing with the source code lines in Pedal? Export each file/line to a big ol' JSON map-of-lists, and have the stack traces reference that instead of the compiled source code. Then we're not rebuilding large strings nor loading them each time we reload the module. We just have them once, loaded separately.