Fix #100: track position while parsing for better errors (#128)
Fix #100: track position while parsing for better errors (#128)

* track position while parsing for better errors

- errors now indicate the position in which they occurred
- the way the parser currently works makes columns hard to track, so
errors will often say "column 1", when they occur elsewhere in the line
- errors in multiline arrays are reported to be on the opening line, due
to the current preprocessing of the input

* accept only IndexError, not unnecessary ValueError

uiri/toml,uiri/toml