literate haskell (.lhs) support missing in htfpp

[jmtd]

It would be great if it were possible to use HTF with literate Haskell. I don't think it is at the moment, for at least one reason: htfpp does not appear to recognise LHS input (nor can it be told via command line option) and so does not detect the test_*/prop_* functions definitions and generates regular Haskell for _thisModulesTests etc

[jmtd]

Bird-style LHS is what I tried first and what doesn't work as described above: using Tex-style LHS works much better: htfpp can correctly read the input Haskell and generates a valid _thisModulesTest etc but does not wrap them in \begin{code}/\end{code}. I suspect that would be an easy feature to add for the most minimal of LHS support.

[skogsbaer]

I'm happy to accept any PR for supporting literate Haskell.