Edit feature TINN for geometrical domain analysis

[Robin Champseix]

Add the triangular interpolation of NN interval histogram feature for the "get_geometrical_features" method.

reference for the feature:
https://www.escardio.org/static_file/Escardio/Guidelines/Scientific-Statements/guidelines-Heart-Rate-Variability-FT-1996.pdf

[Rhenan]

Hi Guys, concerning the geometrical indices, there's a Matlab code with GPL license which seems to compute

• HRV triangular index
• TINN: triangular interpolation of NN

Link to the code

I will check if it is working and try to implement it in the module

Cheers!