Support for literate Haskell

[mgajda]

Add support for using arbitrary preprocessor, and parsing stock .lhs files.

[GildedHonour]

Help is needed, right? I can provide it.

[mgajda]

It should be easy to support GHC_OPTION -pgmL

[mgajda]

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[mgajda]

@dmalkr Can we close this issue yet?

[workshub]

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