compiler options in the prelude

[gelisam]

options like OverloadedStrings, NoExplicitPrelude, etc.

[melrief]

My strategy for this is similar to what we do for modules:

• extract extensions from prelude.hs
• put the list of them in a cache file $HOME/.hawk/cache/extensions
• every time Hawk is executed, load from that file and set them using hint

Currently, the function initInterpreter of System/Console/Hawk.hs loads some default extensions, this should be changed by removing them and loading the cached extensions in $HOME/.hawk/cache/extensions.

[melrief]

I found a solution: the package haskell-src-exts has a function called getTopPragmas that extract the pragmas. I'm starting the implementation of the cache file and then we can easily load that file.