Added option to output directed graphs of the group heirarchy before and after compression (#43)

It outputs nodes and edges information before and after the
compressor has run - these can be visualised in a tool like Gephi

A good way to visualise what the compressor is actually doing!

.gitignore

@@ -2,4 +2,5 @@
 **/*.rs.bk
 *.data
 *.old
-out.sql
+out.sql
+*.csv