Support parsing 4-operation nodes

Apparently one of the memory-related nodes has four operations.  I'm
not entirely sure why, but I'm just going to go ahead and load from it
anyway...
Print memories in flo-canon

The general idea here is that memory nodes don't actually map to an
operation.  This is a bit of a hack: essentially we simply scan
through the list of nodes and print out any memories..
Parse memory nodes

This adds a simple memory test.  Note that it doesn't really test
width inference for memory nodes (as there's not a whole lot of
inference that can be done anyway), but at least it parses
fully-specified nodes correctly.