BRISQUE metric doesn't work

[zakajd]

Describe the bug
I experimented with BRISQUE score today and found it to have nearly 0 correlation with Mean Opinion Scores for TID2013 dataset.
I compared result with pybrisque lib and found that they are very different for real images.

To Reproduce
Steps to reproduce the behavior:

1. Install pybrisque
2. Compute value for 2 attached images
3. Result will be different.

goldhill.gif: 27.8 pybrisque / 111.07 piq.brisque
I01.BMP: 42.1 pybrisque / 95.5 piq.brisque

Expected behavior
I don't know correct value for first image, but for the second it definitely must be ~42, see plot with MATLAB comparison in pybrisque repo

images.zip

[denproc]

The problem is due to data range, used for BRISQUE estimation. pybrisque.BRISQUE().getscore() uses 0-255, while piq.brisque uses 0-1. Changed it at PR.