Hypno simulation

[remrama]

Adds 2 new functions in the yasa.hypno module. See Issue #109.

1. yasa.simulate_hypno - Simulate a hypnogram of arbitrary length. Epochs are generated using a Markov sequence based on probabilities from an epoch-to-epoch transition probability matrix. The transition probabilities can come from yasa.transition_matrix, but I think the real utility is leaving the default trans_probas=None and using a previously published probability matrix based on a large dataset of healthy hypnograms.
2. yasa.hypno_consolidate_stages - This will take a hypnogram and drop it from a 5-stage scheme (W, 1, 2, 3, R) to one of the lower schemes (e.g., W, Light, Deep). Any scheme can be dropped to a lower scheme. This was really just added so that yasa.simulate_hypno could take an n_stages argument.

@raphaelvallat, I placed yasa.hypno_consolidate_stages in the yasa.hypno module for now just to get this merged, but I think it should ultimately be attached as a method to the new Hypnogram class instead.

[codecov-commenter]

Codecov Report

Base: 91.41% // Head: 91.68% // Increases project coverage by +0.26% 🎉

Coverage data is based on head (7da9942) compared to base (b98a4c0).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #110      +/-   ##
==========================================
+ Coverage   91.41%   91.68%   +0.26%     
==========================================
  Files          22       22              
  Lines        2690     2777      +87     
==========================================
+ Hits         2459     2546      +87     
  Misses        231      231              

Impacted Files	Coverage Δ
yasa/hypno.py	97.40% <100.00%> (+1.84%)	⬆️
yasa/tests/test_hypno.py	100.00% <100.00%> (ø)

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[raphaelvallat]

@remrama I am loving this so much! This is gonna be such a great addition to YASA 🚀 Added a few mostly-minor requests, but as usual great work!

[remrama]

@raphaelvallat I think this should be good to go. I ended up merging with master, hope it doesn't mess things up (I rebased once and got into conflict hell, don't know why, but I restarted and was afraid to try that again).

[raphaelvallat]

Awesome work, merging now!