Support eFeatures written in Python

[wvangeit]

It would be handy if the eFEL would support eFeatures written by users in pure python, without requiring a C++ implementation

[orena1]

Hi,
Does it work? Can I use my own python written functions?
Thanks.

[wvangeit]

Yes, more or less. I still need to write some documentation on how to exactly add your own features. But I think it's fairly easy to figure it out based on how this feature was implemented:
https://github.com/BlueBrain/eFEL/blob/master/efel/pyfeatures/pyfeatures.py#L91
As a general rules, when implementing a new feature try to reuse as much as possible the existing cpp features (to detect spikes etc). At some point these will be rewritten in python, but if people now start using their own implementation things might get very messy.
One caveat mentioned here:
#131
The getDistance function doesnt accept python features yet. So it wouldnt work with bluepyopt yet. Let me know if you need that urgently and I will bump it up on my priority list.

[wvangeit]

@orena1
This PR adds the python features to getDistance(): #135

This pypi version includes that code:
https://pypi.org/project/efel/3.0.12/