Update quickstart.rst

Nixing the float: left inducing thing so that it looks better
on RTD.
fixed readthedocs links and updated the quickstart URL
Merge pull request #420 from Foxboron/readme-fix

Fixed readthedocs links and updated the quickstart URL
Add @kenanb's logo to the docs. It's so amazing.

Thanks so much! Read more at:
 http://www.kenanb.com/posts/Hy-Programming-Language-Logo.html