Write a script for generation some hard-coded stuff

[geraldus]

Write script(s) to generate:
for Haskell Doc mode

• a list of Prelude identifiers (ghc -e ':bro Prelude')

for Haskell Completions package

• a list of supported extensions (ghc --supported-extensions)
• a list of supported GHC options (ghc --show-options)
• collect all this stuff in some elisp file
• haskell-doc-prelude-types, haskell-ghc-supported-extensions, haskell-ghc-supported-options should be bound to generated lists
• regenerate this lists once new GHC released

Caveats:

• data declarations should be excluded from :bro Prelude output
• class functions in :bro Prelude output lack of class constraints in type signature, so it should be modified, the easiest method to get valid type signatures would be run :type command for all class functions.

[gracjan]

Fixed in #1334.