Prefer --fast for stack-build (#754)

* Vim scripts shouldn't have hyphens

Especially not ones that will be autoloaded. You can't have a hyphen in
a function name, so autoloading functions based on filename will fail.

* Add g:haskell_stack_build_options, default: --fast

If we're going to use the --fast option, we may as well go the whole 9
yards and let the user configure the 'stack build' flags.

* Create documentation for stack-build options

doc/ale-haskell.txt

@@ -0,0 +1,16 @@
+===============================================================================
+ALE Haskell Integration                                   *ale-haskell-options*
+
+===============================================================================
+stack-build                                           *ale-haskell-stack-build*
+
+g:ale_haskell_stack_build_options           *g:ale_haskell_stack_build_options*
+                                            *b:ale_haskell_stack_build_options*
+  Type: |String|
+  Default: `'--fast'`
+
+  We default to using `'--fast'`. Since Stack generates binaries, your
+  programs will be slower unless you separately rebuild them outside of ALE.
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -41,6 +41,8 @@ CONTENTS                                                         *ale-contents*
       gometalinter........................|ale-go-gometalinter|
     handlebars............................|ale-handlebars-options|
       ember-template-lint.................|ale-handlebars-embertemplatelint|
+    haskell...............................|ale-haskell-options|
+      stack-build.........................|ale-haskell-stack-build|
     html..................................|ale-html-options|
       htmlhint............................|ale-html-htmlhint|
       tidy................................|ale-html-tidy|