Test `.match` with string (uncompiled) regexps.

This was a legacy test which was commented out for some reason, but
tests pass so I'm leaving it enabled.
Add basic documentation for everything.

"Good documentation is good. Bad documentation is better than nothing".
I'm just getting started, and I hoped for having something like DDoc
parse out the documentation automatically for me, but it's ok for now.
Add DDoc header to the source file.

This is a nice practice, I guess, even though I find DDoc's syntax
horrendous.