fwbrasil/clump — pull request #20 by fwbrasil (2014-12-20 19:56:08+00:00)
Title: use a covariant generic for Clumps

@williamboxhall I had compilation issues using ```Clump``` and the solution is use a covariant generic, similarly to the Twitter's Future:

https://github.com/twitter/util/blob/master/util-core/src/main/scala/com/twitter/util/Future.scala#L627