haskell-load: add haskell-goto-first-error

[da-x]

I usually start to fix stuff from top to bottom. This helps finding the first error.

[gracjan]

Hi,

Good function. Is it connected to anything?

[da-x]

I set up my haskell-goto-* bindings to match those of my flycheck setup, which are different from the haskell-interative-mode defaults, which are M-n and M-p for next and prev respectively ever since 2012. I defer on this new binding for @chrisdone to decide.

[gracjan]

We can't burden our users to somehow discover that this exists and then bind the keys themselves.

For this PR to be merged we need:

• user interface element where it is bound (keybinding)
• documentation in haskell-mode.texi
• a unit test case

[da-x]

Added a binding. However, considering that haskell-mode.texi is very lacking around the haskell-process mode, and that the unit tests of haskell-process around UI are practically nonexistent, it's a bit over my head right now to extend on those. Do what you will :)

[bergey]

Finishing this PR is on my list, too.

[gracjan]

Good. Thanks.