Sphinx & Plotting Documentation

[EzryStIago]

Guilty of branch creep.
There are actually two main changes here:

1. Sphinx documentation for read-the-docs
2. PEP8 compliance of plotting.py

Relates to PR 44 in the tutorial: jhenin/SAFEP_tutorial#44

[jhenin]

Fixed a minor compatibility issue with very recent Python.
The BAR_Estimator_Expanded notebook is not just experimental, it currently doesn't run at all (see messages below). I recommend removing it entirely, or into the Legacy directory. EDIT: this is independent from this PR though, so not blocking for merging this.

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
[/tmp/ipykernel_356363/3207517847.py](http://172.27.1.46:8888/tmp/ipykernel_356363/3207517847.py) in ?()
     12         EQ = pd.DataFrame([])
     13         for key, group in groups:
     14             group = group[~group.index.duplicated(keep='first')]
     15             test = subsampling.equilibrium_detection(group, group.dropna(axis=1).iloc[:,-1])
---> 16             EQ = EQ.append(test)
     17         u_nk = EQ
     18     else:
     19         affix=f"{affix}_HardEquilibrium"

[/data/jhenin/lib/miniconda3/envs/safep/lib/python3.12/site-packages/pandas/core/generic.py](http://172.27.1.46:8888/data/jhenin/lib/miniconda3/envs/safep/lib/python3.12/site-packages/pandas/core/generic.py) in ?(self, name)
   6295             and name not in self._accessors
   6296             and self._info_axis._can_hold_identifiers_and_holds_name(name)
   6297         ):
   6298             return self[name]
-> 6299         return object.__getattribute__(self, name)

AttributeError: 'DataFrame' object has no attribute 'append'

[EzryStIago]

@jhenin I've incorporated that change. Are we otherwise clear to merge?