Merge pull request #249 from DanielG/dev-cabal1.16

Fix reading setup-config with Cabal <= 1.16
Merge pull request #250 from DanielG/dev-cabal1.16

Copy ComponentLocalBuildInfo from Cabal-1.18
Merge pull request #251 from DanielG/dev-cabal1.16

Copy readMaybe/readEither from base for backwards compatibility
Add test for no errors case
Suppress empty line
Merge pull request #252 from eagletmt/suppress-empty-line

Suppress empty line
dropping support of GHC 7.2 (#251).
checking if the buffer exists (#256).
fixing a comment.
making ghc-mod-running a global var (##255).
setting sentinel.
using buffer-live-p (#256).
Start migrating Ghc -> GhcMod monad
Ghc -> GhcMod: Browse, Check
Move `convert` to it's own module.
Ghc->GhcMod: finish Browse, Check