Be less strict about prefilter fields

[wmvanvliet]

I'm trying to load EDF file from this dataset: https://physionet.org/content/eegmmidb
In these files, prefilter settings are present in both the normal fields and also in the EDF+ annotations.
For some reason, it was decided that pyedflib should flat out refuse to read such files?
I think that is a bit harsch.

[codecov]

Codecov Report

Merging #114 (40d8da6) into master (bd803bd) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #114      +/-   ##
==========================================
+ Coverage   67.84%   67.87%   +0.03%     
==========================================
  Files           7        7              
  Lines        3623     3614       -9     
  Branches      166      166              
==========================================
- Hits         2458     2453       -5     
+ Misses       1109     1105       -4     
  Partials       56       56              

Impacted Files	Coverage Δ
pyedflib/_extensions/c/edflib.c	66.82% <ø> (+0.03%)	⬆️

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[skjerns]

I understand the annoyance with being so strict about keeping to the EDF specifications. The library we wrap edflib is very strict with regards to these. Even though I would be kind of fine to just read these incorrectly formatted files anyway, I also see why being lose with standards will not help in the long run.

In this particular case: What would happen if prefilter fields have been set to both positions? Which one would be reported?

[wmvanvliet]

In the original code, it would crash. With this PR, the first would be taken.

[skjerns]

fixes #120

thanks @wmvanvliet ! I decided it is indeed a bit harsh to just refuse to load them, and as others seem to have the same problem, I merged your suggestions.