IM3Reader for Perkin-Elmer Nuance

This is a basic reader for the Perkin-Elmer Nuance .im3 format. I don't have access to the file format spec, but I have a fair degree of confidence that the reader works. There isn't much in terms of metadata extraction.
We've had issues with ```MappedByteBuffer``` causing serious problems in certain JVM implementations.  I'd suggest using ```NIOFileHandle``` or ```RandomAccessInputStream``` exclusively in the reader; the caller then has the option of enabling mapped byte buffers under the hood by setting the boolean ```mappedBuffers``` system property (if they feel it's safe to do so).