Add async versions of GhcModInfoPreview && GhcModInfo

[adam-singer]

Would be nice to have async versions of GhcModInfoPreview and GhcModInfo. I'm looking to wire up

set updatetime=1000
autocmd CursorHold *.hs GhcModInfoPreview
autocmd CursorHoldI *.hs GhcModInfoPreview

but the calls tend to have a higher lag time then expected.

[BlackCapCoder]

I ended up doing this, which is better but not perfect:

let moved = 0
autocmd FileType haskell autocmd CursorMoved *
  \ exec "GhcModTypeClear" |
  \ let moved = 1

autocmd FileType haskell autocmd CursorHold *
  \ if moved == 1 |
  \   exec "GhcModType" |
  \   let moved = 0 |
  \ endif

set updatetime=500