Adding key press callbacks instead of setting it.

Calling set(figHandle, 'WindowKeyPressFcn', @callback) as it was done previously would completely kill any previously-defined callbacks on the figure. Adding callbacks via iptaddcallback is cleaner. Unfortunately, this also means we keep adding callbacks if imshowHDR is called repetitively on the same axes! Care is taken to ensure that callbacks for the same axis handles are not added twice.
Ignoring comments when reading XMLs.
Added a slightly modified version of ProgressBar.

Thanks to Richard Stapenhurst!
RGB/XYZ conversion update

Takes in more types of inputs.
Updated comments;
Added XYZ/xyY conversion functions.
str2num calls 'eval'! Can result in _weird_ behavior.