Fix README rendering on PyPI and remove uneeded dependencies

[althonos]

Hi there!

While using this wrapper for the first time I noticed that a. its readme was not rendering on PyPI (see for yourself) and b. that it was using some external dependencies when there was no need to:

• xml.etree.ElementTree can be used instead of lxml.etree, and the accelerated implementation will be used if possible since Python 3.3
• json is simplejson but integrated to the standard library since Python 2.6, which is deprecated, so there is no need to depend on it externally
• html.parser could probably be used instead of html5lib, but because behaviours may differ I actually didn't remove that one