Bring in indpendent url shortener

This replaces a long url at point with a http://ur1.ca shortened url.

This is an indpendent implementation with no dependences.

The idea is that you paste an URL in the post buffer, hit C-c C-s and
the url gets shortened on the fly.
Merge branch 'master' of github.com:mrvdb/twister.el

* 'master' of github.com:mrvdb/twister.el:
  Update README.md