Platform-Variants: removed

  - Platform/hugs: support for Hugs is (temporarily) given up.
  - Platform/haddock: no seperate version for haddock documentation tool

Rationale:
  - In the current project's state it seems to be not a bad idea to
    waste (wo)manpower on a niche like support for hugs.
    This is not about dependency on GHC specific features. The argument
    is about (not) having untested/unmainained code in the codebase.
    If support for hugs becomes an issue in the future the deleted code
    might well be recovered from the version control system.
  - I think it is a bad idea to generate haddock documentation from (fake)
    code that is not actually run in production. There needs to be a
    better solution.