Move conversion between each image type to imcast. * im2double.m, im2int16.m, im2single.m, im2uint16.m, im2uint8.m: move code into imcast. Fix several small bugs mainly dealing with indexed and logical images, small precision for Matlab compatibility, and increased performance. Expanded documentation. Added new tests. * imcast.m: implement the conversion between each image type instead of being a wrapper around functions for each conversion. This reduces code duplication, and places all very similar (but not equal) code together so that a bug fix in one can be easily notices that requires application in others. Expand documetation. Add more tests. * private/imconversion.m, private/im2float.m: remove no longer necessary function since this has all been moved to imcast. * COPYING: remove license for private/im2float.m and private/imconversion.m. * NEWS: make note of bug fixes for this functions.