Move image-related code to its own Image class
Make Image determine the type of the file to write to from the path's extension
Implement writing an Image to a raw .bin file
Make ilium look at the extension of the input file to figure out what to do
Implement reading from a binary file and then writing to another file
Implement merging of two images with the same parameters
Accept any filename containing ".bin" as a binary file
Rework directory structure to follow go standards

http://golang.org/doc/code.html describes how code should be structured.
Add LICENSE and README files
Split off .bin merge functionality into its own executable
Decode Spectrum directly instead of going through encoding.binary.Read()
Pull the read IO from Spectrum into Weightedli
Pull the read IO from weightedLi into ReadImageFromBin()
Turn Spectrum.SetFromBytes() into MakeSpectrumFromBytes() for consistency
Add command-line switches for output directory and output extension