Find a better way to apply docrepr config options

[ccordoba12]

docrepr defines some configuration options in its __init__.py file:

https://github.com/spyder-ide/docrepr/blob/master/docrepr/init.py#L20

However, for these options to take effect, you need to do two imports, like this:

import docrepr
from docrepr.sphinxify import rich_repr

We need to find a better way to do this (but at the moment I can't think of a good one :-).

The problem is that without loading those options, things like MathJax don't work correctly.

Pinging @SylvainCorlay about it.