Replaced a few calls to stringr with stringi (which has to stay for unicode encoding function). Not likely that people won't have stringr, but makes the dependencies a little better.

Track # of result groups in regex result data frame as idx$pass. Refactored span collating.

Global matching implemented inside run_regex(), nothing above initial regex matching works now.

- Removed knitr parameter
- Add result_only (not in knitr)
- Soft deprecate kntir parameter
- Separate group.css from other css styles

Fixes issues with adding <span> and </span> around zero-length groups and more generally groups that start and end at the same index.

Ensures that g00 wraps all others, then at index with close/opens, closes open groups first before opening new groups.

- Colorize regex in view_regex
- Use exact=TRUE param to show all backslashes in wrap_regex
- Rename wrap_span -> wrap_result