Add travis automation for building and running the benchmarks

You can check the current build status here:
https://travis-ci.org/errge/Haskell-Pipes-Library/builds/11053151

Both architecture (amd64 and i686) fails, because the benchmarks fail.  This is not a travis issue, it fails on my home machine too.

Using Ceh, so we can get GHC 7.6.3 with a lot of packages and on both architectures.  Travis only supports GHC 7.4 and only on amd64.

More about Ceh, if you are interested: http://www.gergely.risko.hu/fpafternoon-zurich-20130829/ceh.html