Not doing this makes having GhcModT pretty pointless as users of the
library wouldn't be able to use custom inner monads as evey function for
dealing with GhcModT's would be constraint to (GhcModT IO) thus only
allowing IO as the inner monad.
Having to call `findCradle` and `initializeFlagsWithCradle` everywhere
we interact with ghc-mod's API doesn't seem very Haskell-like to me I
think we should provide a Monad that has a run function that already
does all those tedious tasks for us.
The `GhcMod` monad is basically a wrapper around `RWST r w s IO` with an
instance for `GhcMonad`
Having a `Reader` allows us to pass `Options` to runGhcMod and not have
to worry about passing it everywhere, `Cradle` is also stored in the
reader environment on initialization.
Writer and State are just there for future use.
I've included a `toGhcMod` function that turns a `Ghc a` into a `GhcMod
a` this will make it easy to transition everyting to using the `GhcMod`
monad instead of `Ghc` without breaking the build or test suite for
extended periods of time.
Conflicts:
ghc-mod.cabal
Kazu Yamamoto