Notes on Tom Lord's rx regexp package.

API info nodes should give C prototypes. re_compile_pattern doesn't.

Many thread-reentrancy problems:
    - syntax var is a shared global. Needs to be passed as arg to 
      pattern compiler -- which could easily be done by simply having
      the client pre-set the pat->syntax field.

    - regs field should not be a part of the pattern -- you can't
      use the pattern in multiple concurrent matches.

      Similarly for pat->no_sub, pat->not_bol, pat->not-eol. These fields are
      properly part of of the client's request, not the pattern.
