Remove trackComments, add onComment option

trackComments was too obscure and complicated, and not all that useful.
Bump version to 0.0.2
Fix regexp detection after void/typeof/instanceof/delete
Attach position information to errors
Export the tokenizer
Small fixes noticed while going over the when writing loose parser
Add a loose parser

For getting a halfway meaningful AST out of code that may contain
syntax errors.

Use case: analyzing code as the user is editing it.
[loose parser] Make expect check two tokens ahead if it fails to find its target
[loose parser] Add note about imprecision
[loose parser] Support tabSize option
[loose parser] Several small tweaks
Upgrade Esprima
[loose parser] Fix bug in argument list parsing
[loose parser] Revise strategy for forcing token consumption

It's easier and more flexible to simply handle it at the call site.
[loose parser] Use ✖ rather than question mark for placeholders

This way, attempts to re-parse the pretty-printed code won't
be confused by the question marks.
[loose parser] Fix typo
[loose parser] Improve recovery from unterminated strings and regexps
Add testAssert() for arbitrary tests; fix skinLineComments() passing off-by-1 character to onComment(slice(.., end))
Add walk.findNodeAt utility
[loose parser] Refine block-closing heuristics, add expression-continuing heuristics