Add integration with Tasty

[martijnbastiaan]

It would be nice if we could publish a package docktest-parallel-tasty that would provide Tasty integration, i.e., that would yield a TestTree. Something like:

tastyFromCabal :: String -> [String] -> IO TestTree
tastyFromLibrary :: String -> Config -> IO TestTree
tastyFromCabalWithConfig :: Library -> [String] -> IO TestTree
tastyFromLibraryWithConfig :: Library -> Config -> IO TestTree

Granularity is an open question for me: would we make each module a TestTree or each example?