man: update examples to use spec command
more TODO
Rpm.hs: new simply Fedora Packaging and use findProgramLocation to check available

- see https://fedorahosted.org/fpc/ticket/194
- drop %common_summary and %common_description
- drop %ghc_package, %ghc_description, %ghc_devel_package,
  %ghc_devel_description, %ghc_devel_post_postun, and %ghc_files
- trySystem now checks if program available before use
bump to 0.8.0 and update news