Version 0.5.4

New version fixing a major bug in cross-correlation, minor bugs in stdlib.imgql related to arithmetic operators, and improving the percentiles operator.

NOTE: on windows, if you get a DLL / PINVOKE error while loading images, please install the visual studio 2015 redistributable framework from microsoft:

https://www.microsoft.com/en-us/download/details.aspx?id=48145