inventories post-processing tool

Just a misc tool that will aid quick, easier analysis of agent inventories.  The README should explain everything.  I wrote it in go - sorry.  We can revisit later and rewrite in python or other lang if this kind of thing becomes a part of the standard cyclus workflow.  But it exists in go for now and works.  If people want to use the tool, but don't want to build it, I can provide a statically linked binary that they can just use.