Added 7 more EMG onset detectors

[tostasmistas]

• Modified emg.py to include 7 more onset detectors
• Modified plotting.py to also plot the processed EMG signal
• Added a new EMG signal example with more activations and rest sequences

[capcarr]

Hi @tostasmistas
Thanks for your contribution. I'll review and merge in the following days.
Would you like to also to write a short chapter about EMG signals for the documentation (http://biosppy.readthedocs.io/en/latest/tutorial.html#electromyogram)?

[tostasmistas]

Hi @capcarr
If the contribution requires any fix let me know.
Regarding the short chapter, were you thinking of something like this?

Electromyogram (EMG) signals are a measure of the electrical activity of muscles. There are two types of sensors that can be used to record this electrical activity, in particular surface EMG (sEMG), measured by non-invasive electrodes, and intramuscular EMG. Out of the two, sEMG allows for non-invasive electrodes to be applied at the body surface, that measure muscle activity. In sEMG, contact with the skin can be done with standard pre-gelled electrodes, dry Ag/AgCl electrodes or conductive textiles. Normally, there are three electrodes in an sEMG interface: two electrodes work on bipolar differential measurement and the other one is attached to a neutral zone, to serve as the reference point. After being recorded, this signal can be processed in time, frequency and time-frequency domains.
In an EMG signal, when the muscle is in a relaxed state, this corresponds to the baseline activity. The bursts of activity match the muscular activations and have a random shape, meaning that a raw recording of contractions cannot be exactly reproduced. The onset of an event corresponds to the beginning of the burst.

[capcarr]

Thanks for the text @tostasmistas