Log Message:
Update to 0.19. Update HOMEPAGE and MASTER_SITES. Allow python-3.

--0.19--
Released June 10, 2014

* Moved issue tracking to github and the main website to mpmath.org.
  Several URLs and issue numbers were updated in the documentation
  (Sergey B Kirpichev)
* Enabled automatic testing with Travis CI (Sergey B Kirpichev)
* Fixed many doctest issues (Sergey B Kirpichev)
* Converted line endings to LF (Ondrej Certik)
* Made polyroots() more robust (Ondrej Certik)