Using sphinx autodoc instead of duplicating effort

Notes:

 * Makes the documentation more complete
 * No need to copy paste from the original source
 * we can focus on making the original doc strings more complete
 * we can focus on adding examples etc

Reason for change:

 * many functions were missing in this documentation (and not even mentioned in the upstream selenium docs, like set_window_size etc. Now they are visible. And all new methods, attributes and properties will show up in the docs automatically :) neat right?