Removal of XML parsers: pyRXP, 4suite

* Removes pyRXP from the mandatory dependencies (#1797)
* Removes 4suite (their website says to not use it anymore :haircut:)
* Some PEP8/257 :heart: 
* **NOTE** if pyRXP is installed, it will still be used instead of lxml. If anything breaks, write more tests.
1: D400 First line should end with '.', not 'o'
1: D205 Blank line missing between one-line summary and description
4: I102 copyright year is outdated, expected 2014 but got 2011
188: D400 First line should end with '.', not 't'
200: D400 First line should end with '.', not 'r'
212: D400 First line should end with '.', not ','