remove weights_ member from setset
add constructors
add richcompare and ~
fix dump(), and arrange test.py following illion_test.cc
rename illion_test.cc to test.cc
fix dump()
add isdisjoint, issub|superset
fix some error messages
add minimal, maximal, hitting, intersection
add |, -, *, ^
add |, -, *, ^
add /, %, (non)subsets, (non)supersets
add clear(), copy(), len()
small modifications