Add `stack runhaskell`

[ndmitchell]

As an alias for stack runghc. I keep mistyping it, and both are valid GHC supplied binaries.

[borsboom]

We're mostly sticking with using ghc in the subcommand names (e.g. stack ghci instead of stack repl, etc.). That said, no real objection to adding the alias. A PR would be welcome.

[ndmitchell]

Note that repl is a bad name since it isn't a GHC command, while runhaskell is a GHC command and has been for many years (however, for cabal compat, repl is probably useful)

[rvion]

I also think stack repl is a good idea, both for discoverability and cabal compatibility

[rubik]

The PR has been merged, this should be closed.

dd554f5