Updates for changes in GHC API. Fixes #24.

Updates to GHC API Pretty.showDoc
Changed showDoc mode 1 to showDoc mode 0
Add support for cabalized projects
Add handling of Cabal errors
Support running from cabal package subdirectories
Add cabal version info to help message
Cabal workaround inplace library dependency
Filter out -Werror from cabal GHC options
Switch off cabal support for older GHC versions
Search for .cabal file from target file directory

Currently search for .cabal file is done from current directory
which requires that hdevtools is run from package directory or
it's subdirectory which is not always easy to achieve when
hdevtools is run from inside editor.
This fix changes search logic so that .cabal file is searched
starting from target file's directory (for commands that have
target file) or from current directory for other commands.
Pass path to cabal config from client to server.

This allows running hdevtools first time from
anywhere, not just from cabal package's
(sub)directory.
Merge branch 'ghc7.7' into cabal-support
Adds support for ghc7.8
Merge branch 'cabal-support-ghc7.8' of https://github.com/schell/hdevtools