Add .travis.yml file

Just uses the existing tox config as described in
<http://borntyping.com/posts/tox-and-travis-ci.html>.

This fixes #299. I took this route rather than @mitya57's
suggestion because we get better test coverage with tox's
config (more dependencies are installed) and I can't see
mirroring that here when we can just reuse it.
Update .travis.yml

Add install of libtidy dependancy. Forgot about that.
Added some badges to the README

Using shields.io for generating badges.
Emphasized proper use of reset method in docs.

This is related to waylan/Python-Markdown#305.
Merge pull request #306 from brownhead/master

Emphasized proper use of reset method in docs.
No assertIs in Python 2.6. Fixes #294
Skip a weird PHP test.

I can't make out what this PHP test is trying to accomplish. From my point of view, our output is fine. So we skip this test.
Add smarty to extensions for attr_list test

To make it easier to notice (and fix) the failure.