Add lineno

[mingodad]

Add line number and column to error messages

[ChrisHixon]

I like the idea of adding line number tracking, but I don't think this pull request does this in a complete/correct way.

[mingodad]

It's a start point that at least for the few cases I'm trying it now is showing a useful result, if we can nail down the flaws that you are seeing I also would like to have the file name on the error message, my editor can jump to the error line, column when the message start with the filename:

<filename>:line:column message

[ChrisHixon]

I've only looked at the diff here, but I think it misses some cases where a newline can occur, like inside a LIT. Perhaps more critical , offset is reset from the stack during backtracking, so I think the line:col tracking would need to be reset as well when backtracking (so saved on the stack). I think line:col tracking would have to follow offset through all changes to it or there will be cases where the tracking is incorrect. I dont think I like the idea of putting all this kind of line:col tracking inside the parser VM anyway. A better and simpler approach might be to find the error's line and col from the error_offset when an error is printed; just count the number of newlines that occur before error_offset for line number, and calculate the col looking back to the nearest newline position.