- moved haskell sources to src as it's a standard convention

Perhaps my grep-foo is weak or I'm laz, but the fact that everything resides at the top-level directory makes it more difficult to parse files for patterns. For example, I either have to add *.hs to patterns and/or explicitly include the individual module directories to avoid searching for unrelated files (even more problematic within a sandbox). Also, I think it's pretty standard to have  `src` directory with your sources.