Fix a small bug in set_noise_var in Blast class

If the `noise_var` argument passed to set_noise_var was 0.0 an exception
was raised this exception should be raised only for negative values.
Implement _calc_receive_filter in GMDMimo
Implement a function to calculate the SU SINRs

Implement the `calc_post_processing_linear_SINRs` and
`calc_post_processing_SINRs` that calculate the SINRs of the streams of
one user.
Improve the calc_post_processing_linear_SINRs

The argument `G_H` in calc_post_processing_linear_SINRs can now be
either a number or a numpy array.
Implement calc_linear_SINRs and calc_SINRs methods

Implement the `calc_linear_SINRs` and `calc_SINRs` methods in the
MimoBase class.
Implement calc_linear_SINRs in the Alamouti class
Small change in the SINR calculation tests

Consider as correct if the calculated SINRs for the GMD MIMO scheme are
equal up to 1 decimal place to the expected values (it was 2 decimal
places before).
Merge branch 'SINR_MIMO_Calc'

This branch contains the functions to calculate the single user post
processing SINRs.