Example for use of Kleisli functions.
Remove utilM overloading

Looks like it should be utilM_ instead. I didn't hit any problems with
this, just noticed that it was very strange to be overloading on whether
an implicit was found.
Add `leftAs` and `rightAs` to Bifunctor syntax

Symmetric with `as` from the Functor syntax.
Merge pull request #674 from puffnfresh/remove-untilm-overloading

Remove utilM overloading
Merge pull request #675 from puffnfresh/bifunctor-as

Add `leftAs` and `rightAs` to Bifunctor syntax
Merge pull request #666 from justjoheinz/fix/kleisliusage

Example for use of Kleisli functions.