MAINT: use scipy.special.xlogy
fixed entr so entr(0) = 0
Revert "fixed entr so entr(0) = 0"

This reverts commit f1824089b598b104dfa2bcc9d3fc1fe4ac0eaa4c.
Merge pull request #53 from argriffing/use-xlogy

MAINT: use scipy.special.xlogy for entr and kl_div