First pass at optimizing ale to autoload (#80)

* First pass at optimizing ale to autoload

First off, the structure/function names should be revised a bit,
but I will wait for @w0rp's input before unifying the naming style.
Second off, the docs probably need some more work, I just did some
simple find-and-replace work.

With that said, this pull brings major performance gains for ale. On my
slowest system, fully loading ale and all its code takes around 150ms.

I have moved all of ale's autoload-able code to autoload/, and in
addition, implemented lazy-loading of linters. This brings load time on
that same system down to 5ms.

The only downside of lazy loading is that `g:ale_linters` cannot be
changed at runtime; however, it also speeds up performance at runtime by
simplfying the logic greatly.

Please let me know what you think!

Closes #59

* Address Travis/Vint errors

For some reason, ale isn't running vint for me...

* Incorporate feedback, make fixes

Lazy-loading logic is much improved.

* Add header comments; remove incorrect workaround

* Remove unneeded plugin guards

* Fix lazy-loading linter logic

Set the wrong variable....

* Fix capitialization

ale_linters/haskell/ghc.vim

@@ -58,7 +58,7 @@ function! ale_linters#haskell#ghc#Handle(buffer, lines)
     return output
 endfunction
 
-call ALEAddLinter('haskell', {
+call ale#linter#Define('haskell', {
 \   'name': 'ghc',
 \   'output_stream': 'stderr',
 \   'executable': 'ghc',
@@ -66,7 +66,7 @@ call ALEAddLinter('haskell', {
 \   'callback': 'ale_linters#haskell#ghc#Handle',
 \})
 
-call ALEAddLinter('haskell', {
+call ale#linter#Define('haskell', {
 \   'name': 'stack-ghc',
 \   'output_stream': 'stderr',
 \   'executable': 'stack',