remove dependency on networkx
handle inverted edges, (u,v) as well as (v,u)
rename private methods in illion.py by prepending _
use unittest in test.py
take default weight value in optimize()
take default weight value in optimize()
small modifications in setup.py
add larger and equal
indentate test.py
do refactoring in test.py
small modifications in optimize()
divide illion.py into illion/setset.py and illion/graphset.py