Fixes building tarballs.
We also include the test suite, the original stand-alone Makefile and
READMEs.

* This was a combination of conversion loss and a too small color map.
* The test suite was actually broken for Unicode since we have to
  `setlocale(LC_ALL, "")` for the libc Unicode handling functions
  to work as expected. SciTECO already did that.
* Added test cases for plain Unicode (Cyrillic) characters in the
  regexp and for character ranges.

This allows you to pass in additional flags like `-DREG_DEBUG`.
terex is *not* built with assertions by default unless you define REG_DEBUG.

Allows you to set up a callback that's invoked repeatedly during
matching. If it returns non-0 matching will abort and REG_EINTR is
returned.
Allows you to interrupt long-running regexp executions that would
otherwise block the UI or hang the entire application.

* Perhaps I am also obliged to document what I changed in the copyright header?
  Not sure.
* The license header doesn't necessarily have to be reproduced in binary
  distributions.

The headers still define regfree() and regerror() functions,
but they shouldn't collide with libc unless you include the POSIX regex.h.

Also tere_free() can now be called on nullified regex_t objects, which
eases error handling a bit.

I put them into longest() as well, but it appears that both find() and cfind()
will always try shortest() first and should abort if that returns NULL.

* So you can anchor executions of already compiled patterns.
  In principle REG_BOSONLY could also be handled by the same code.
* Required by SciTECO.
* Test suite has been fixed and extended.
  The test program now takes getopt() style short arguments to specify flags.