Add a few `{-# LANGUAGE CPP #-}`s

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
`M-x untabify` & `M-x delete-trailing-whitespaces`

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Refactor & modernize `hpc.cabal` to `cabal-version>=1.10`

The `build-depends` have been updated to match the library version
ranges shipped with the GHC versions for which compilation currently
succeeds.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Add `README.md` and `.travis.yml` script

This enables testing (or rather testing the packages builds) for all
released GHC versions this package is expected to work with.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>