Merge pull request #55 from bluescreen303/master

Cabal2Nix/PostProcess.hs: add version-unlock patch for trifecta
src/Cabal2Nix/Flags.hs: link hslua against the system's lua library
Postprocess: github-backup depends on git
Cabal2Nix/Name.hs: map libusb-1.0 to 'libusb'
Flags.hs: system-lua support in HsLua is broken
Add support for new 'testTarget' attribute.
PostProcess.hs: configure testTarget for 'dns' library
cabal2nix.cabal: tentatively bump version number to 1.55
Flags.hs: Revert "system-lua support in HsLua is broken"

The new hslua version fixes this issue.
HList needs 'diff' in $PATH during the test suite.
README.md: don't refer to the obsolete $NIXPKGS_ALL environment variable
PostProcess.hs: fix ghc-mod post-process hook
Flags.hs: enable wireless support in xmobar
Map 'IL' to 'libdevil'.
src/Cabal2Nix/Hackage.hs: fix hlint warning
Add support for meta.hydraPlatforms attribute.
cabal2nix.cabal: tentatively bump version number to 1.57
PostProcess.hs: modern versions of happy require alex as a build tool
PostProcess.hs: configure noHaddock hook for markdown-unlit
PostProcess.hs: update postInstall hook for ghc-mod