cleanup of the category of Coxeter groups

[chapoton]

with partial pep8, and fixing the last py3 doctest

[chapoton]

New commits:

​0df92e7

cleanup of the category of Coxeter groups

[tscrim]

Nitpick for spaces for index_set (since you are doing PEP8 cleanup on that line):

def weak_covers(self, side='right', index_set = None, positive=False):

LGTM otherwise and you can set a positive review once changed.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​7e11646

trac 26530 detail

[chapoton]

done, thanks. Setting to positive