added importjs fixer

- added tests for fixer functions
- added docs

autoload/ale/fixers/importjs.vim

@@ -0,0 +1,24 @@
+" Author: Jeff Willette <jrwillette88@gmail.com>
+" Description: Integration of importjs with ALE.
+
+call ale#Set('js_importjs_executable', 'importjs')
+
+function! ale#fixers#importjs#ProcessOutput(buffer, output) abort
+    let l:result = ale#util#FuzzyJSONDecode(a:output, [])
+    return split(get(l:result, 'fileContent', ''), "\n")
+endfunction
+
+function! ale#fixers#importjs#Fix(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'js_importjs_executable')
+
+    if !executable(l:executable)
+        return 0
+    endif
+
+    return {
+    \   'command': ale#Escape(l:executable)
+    \       . ' fix'
+    \       . ' %s',
+    \   'process_with': 'ale#fixers#importjs#ProcessOutput',
+    \}
+endfunction