Replace reldir="extensions" with location="inx"

As described on the Updating your Extension for 1.0 wiki page, replacing reldir="extensions" with location="inx" in each .inx file gives the user the flexibility to install the extension in any arbitrary subfolder. That substitution is the key part of this pull request. While I was at it, though, I made a few minor changes to pathops.py to appease Pylint (mostly use of len and indentation issues).