added mandelbrot sample and removed some ghc warnings

Hi - maybe you are interested in this small additional example (you kind of asked) - there are two images included so maybe you want to use them

I use sublime-haskell to do my editing and cabal-sandboxes to keep my system clean, so I did add some items into .gitignore to keep things clean.

Additionally sublime-haskell (ghc -Wall) had some minor warnings for me (missing type-declarations and one not-needed include) and so I solved this small issues - hope you don't mind - I don't think that this can break anything really (surely does not break my sample).