improvements for Wifi shield

[robertoostenveld]

while reading through the code to find out how it deals with the (mostly undocumented) wifi shield, I have made some updated to the documentation.

[robertoostenveld]

Furthermore, testing the code with wifi+cyton I also made some small code changes. It now runs, but the time courses are not yet correct, i.e. all numbers are the same, and don't match the signals I can see with the same hardware in the OpenBCI GUI application.

[codecov-io]

Codecov Report

Merging #119 into master will decrease coverage by 0.16%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master    #119      +/-   ##
=========================================
- Coverage   37.46%   37.3%   -0.17%     
=========================================
  Files           9       9              
  Lines        1588    1595       +7     
=========================================
  Hits          595     595              
- Misses        993    1000       +7

Impacted Files	Coverage Δ
openbci/ganglion.py	13.86% <ø> (ø)	⬆️
openbci/cyton.py	47.13% <0%> (-0.38%)	⬇️
openbci/wifi.py	20.65% <0%> (-0.19%)	⬇️

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