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

autoload/ale/util.vim

@@ -0,0 +1,65 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: Contains miscellaneous functions
+
+function! s:FindWrapperScript() abort
+    for parent in split(&runtimepath, ',')
+        " Expand the path to deal with ~ issues.
+        let path = expand(parent . '/' . 'stdin-wrapper')
+
+        if filereadable(path)
+            if has('win32')
+                return path . '.exe'
+            endif
+
+            return path
+        endif
+    endfor
+endfunction
+
+let g:ale#util#stdin_wrapper = s:FindWrapperScript()
+
+" A null file for sending output to nothing.
+let g:ale#util#nul_file = '/dev/null'
+
+if has('win32')
+    let g:ale#util#nul_file = 'nul'
+endif
+
+" Return the number of lines for a given buffer.
+function! ale#util#GetLineCount(buffer) abort
+    return len(getbufline(a:buffer, 1, '$'))
+endfunction
+
+" Given a buffer and a filename, find the nearest file by searching upwards
+" through the paths relative to the given buffer.
+function! ale#util#FindNearestFile(buffer, filename) abort
+    return findfile(a:filename, fnamemodify(bufname(a:buffer), ':p') . ';')
+endfunction
+
+function! ale#util#GetFunction(string_or_ref) abort
+    if type(a:string_or_ref) == type('')
+        return function(a:string_or_ref)
+    endif
+
+    return a:string_or_ref
+endfunction
+
+function! ale#util#LocItemCompare(left, right) abort
+    if a:left['lnum'] < a:right['lnum']
+        return -1
+    endif
+
+    if a:left['lnum'] > a:right['lnum']
+        return 1
+    endif
+
+    if a:left['col'] < a:right['col']
+        return -1
+    endif
+
+    if a:left['col'] > a:right['col']
+        return 1
+    endif
+
+    return 0
+endfunction