Compatibility with base 4.7.0.0

base 4.7.0.0 entirely removes `mkIntConstr` from `Data.Data`, preferring
`mkIntegralConstr`. This has been available since base 4.2.0, so I've
used -XCPP to use mkIntegralConstrr if possible.
Fix build on GHC 7.6

This commented out #def seems to still trigger the CPP macros.
Adding myself to LICENSE
Always depend on syb

For base < 4, base simply depends on syb. If we explicitly depend on it,
we have nothing to lose. The flag is needlessly complicating the cabal
file.
Add -XCPP to the list of extensions in the cabal file
Mention Github in .cabal file