Use a more robust html parser (lxml) to avoid parsing issues.

ElementTree was failing with the following message:

    xml.etree.ElementTree.ParseError: not well-formed (invalid token)

+ move all imports at the beginning
+ move the main stuff at the end
+ fix some pep8 space issues.
Add lxml and python-cssselect to the PKGBUILD.
Use mkaurball since .AURINFO file seems mandatory now.

https://wiki.archlinux.org/index.php/AURINFO