Rewrite patch with pyquery for robustness

Not all HTML can be parsed with a strict XML parser. Some
Sphinx extensions insert HTML from sources outside of the
local author's control (sphinxcontrib-embedly, for example).
In order to support RSS feeds with valid links and the
embedded content from these extensions, use a more forgiving
HTML parser when patching the links.

Change-Id: I045e338289b63832315210b31a7188d5c6ab6570
Fix handling of read more links

Replace the string-based patching with PyQuery calls that preserve the
proper structure of the remaining nodes.

Change-Id: If9fcf3b7964e26fda16c7cdb3087e2ca1d0e47ba
Do not encode text before passing to PyQuery

Encoding the body of the document breaks some characters like
apostrophes.

Change-Id: I362aa60204fc77d1893e89e8efc61b78e2f063ed
Merge pull request #44 from dhellmann/pyquery

Rewrite patch with pyquery for robustness