Haskell-backend: Do not generate trailing whitespace.

Removed trailing white space in Haskell source code strings, such that
the generated .hs files do not have trailing whitespace.
Haskell backend: top-level type signatures in generated code.

Missing top-level type signatures generate a warning.
Added all missing top-level sigs.
Haskell backend: _ for unused variables in generated code.

To make the generated Haskell code error free, use _ or _ident for
unused bindings everywhere.
Set version of happy and alex

There is some incompatibility that make packages generated with older
version of alex/happy incompatible with ghc 7.8. (Yes, I'm talking about
source packages! go figure...)

This ensure that we use a modern version of the tools when generating
the package.
Reverting last change on the version of happy and alex

Cabal put the files generted by alex and happy in the source package
generated by sdist, which mean that there is no need for the tools to be
run when you install the package. But it turns out that cabal will still
complains if you don't have the right version when you do `cabal
install`!!
Bump version
Change License from GPL to GPL-2

This is the version corresponding to the LICENSE file.
Add repsitory information in the cabal file
Merge pull request #109 from andreasabel/master

Haskell backend: generate warning free code.
Add regression test for issue #110
Fix issue #110
Remove deprecated and unused import of System.Cmd
Remove autogenerated file accidentally added
Make haskell makefile remove generate ComposOp.hs

Fix #102
Fix introduced regression

Correctly escape single quote *'*
Add a changelog where cabal can find it
Increment version number
Convert some spec to doctest
Make cabal run doctests
Fix doctest for renderCharOrString