combination iterator inherits from std::iterator
adds basic combination test
builds combinations test
tests enum postfix++
adds enumerate == and postfix ++
tests zip postfix++
adds zip postfix++
uses zip == instead of !(!=)
adds zip ==
uses range == in test
adds == to range
tests for postfix ++
adds range postfix ++
fixes enumerate test
tests accumulate ==
adds == to accumulate
tests accumulate postfix ++
adds accumulate postfix ++
adds chain test for ==
adds chain ==