use alias method for second draw from multinomial
fix package
fix package
fix comment
added CanTraverseKeyValuePairs implicit for Counters
Merge pull request #259 from gabeos/master

added CanTraverseKeyValuePairs implicit for Counters
synchronize alias sampling and add test
clean up headers
Merge pull request #258 from jacobandreas/master

Implement alias sampling for Multinomials