Test hMRI processing

Testing some functions and features from the hMRI toolbox

hmri_proc_zero2nan_test.m

Proper test function fro the hmri_proc_zero2nan.m function.

Making sure that the conversion of 0's into NaN's, for data format that can represent it (float32 and float64), is not messing up the data. Conversely, nothing bad should happen to the (unsigned) integer data, which do not represent NaN.

References:

• hMRI toolbox: https://hmri.info/
• mask issue & fix: hMRI-group/hMRI-toolbox#50