Removed the need to install lxml. This package can be used as a CSV imported perfectly fine without that requirement (which requires compilation and the necessities that come with that) and therefore it is now an optional extra.
- Removed from requirements.txt
- Moved module level lxml imports to the method level; ideally the XML fields should be split out into another module to avoid this.
- Moved lxml requirement in setup.py from install_requires to extras_require.