Also adds regexplain_web()

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.

and restore when input$pattern is empty

- Use global option regexplain.addin.max_lines (default 100)
- Give hint on warning about option
- Always use unique lines in selection

regexplain.debug.gadget.(text|pattern|replacement)