WIP: Regexp#exec implementation now works for basic cases.
Merge branch 'master' into finish-regexp
RegExp#exec now does successive matching.

- Properly set the lastIndex value.
- Make sure count PCRE wrapper is non-negative.
Merge branch 'master' into finish-regexp
Fixes a few typos

- No such thing as test 252
Improves RegExp literal lexing. (Fixes #7)

- Whitespace within the regexp is now allowed.
- Escaped forward slashes (/) are now allowed.
- Use the previous token to decide between a division and a RegExp
  literal. This reasoning works in the majority of cases but there are
  exceptions that will need a revisit (e.g.  ++).
- Can now parse underscore.js and the test262 harness without errors.
Improvements to RegExp#exec and String#match
Merge branch 'finish-regexp'