cabal-helper-0.7.3.0: Simple interface to some of Cabal's configuration state used by ghc-mod

# cabal-helper-0.7.3.0: Simple interface to some of Cabal's configuration state used by ghc-mod

`cabal-helper` provides a library which wraps the internal use of an executable to lift the restrictions imposed by linking against versions of GHC before `7.10`. This has the pleasant side effect of isolating the user from having to deal with Cabal version changes manually as `cabal-helper` can simply recompile it's helper program automatically as needed.

`cabal-helper` uses a wrapper executable to compile the actual cabal-helper executable at runtime while linking against an arbitrary version of Cabal. This runtime-compiled helper executable is then used to extract various bits and peices from Cabal's on disk state (dist/setup-config) written by it's configure command.

In addition to this the wrapper executable also supports installing any version of Cabal from hackage in case it cannot be found in any available package database. The wrapper installs these instances of the Cabal library into a private package database so as to not interfere with the user's packages.

Furthermore the wrapper supports one special case namely reading a state file for Cabal itself. This is needed as Cabal compiles it's Setup.hs using itself and not using any version of Cabal installed in any package database.

`cabal-helper` can compile with `Cabal >= 1.14` but requires `Cabal >= 1.16` at runtime.

Modules

- Distribution
  - Distribution.Helper