fix mask reading issue
Fix issue in diff_tomo relative to the mask.
Adding rayonix mx series detectors

Adding rayonix mx series detectors:
* mx225
* mx300
* mx325
Documentation: http://www.marresearch.com/pdf/Brochure.mx.pdf
Merge pull request #81 from gbenecke/patch-2

Adding rayonix mx series detectors
Merge remote branch 'origin/master' into HEAD