Fix compilation issues when using GHC 7.0.1

According to the 7.0.1 Release Notes
<http://www.haskell.org/ghc/docs/7.0.1/html/users_guide/release-7-0-1.html>,
the via-C backend was deprecated. Passing the -fvia-C flag was causing
compilation to fail.

Also, relax the dependency requirements on base, bytestring.
Add Show constraint next to Integral which is needed from GHC >7.4.1
eliminate a warning, do not use Foreign.unsafePerformIO
add git source repo to .cabal file
Merge pull request #1 from prezi/master