Add rails_best_practices handler (resolves #655) (#751)

* Move FindRailsRoot() to more general location

* Add rails_best_practices handler (resolves #655)

* Update documentation for rails_best_practices

Also add brakeman to *ale* documentation.

* rails_best_practices: allow overriding the executable

* rails_best_practices: format help correctly

* rails_best_practices: capture tool output on Windows

autoload/ale/handlers/rails_best_practices.vim

@@ -0,0 +1,6 @@
+call ale#Set('ruby_rails_best_practices_options', '')
+call ale#Set('ruby_rails_best_practices_executable', 'rails_best_practices')
+
+function! ale#handlers#rails_best_practices#GetExecutable(buffer) abort
+    return ale#Var(a:buffer, 'ruby_rails_best_practices_executable')
+endfunction

autoload/ale/ruby.vim

@@ -0,0 +1,22 @@
+" Author: Eddie Lebow https://github.com/elebow
+" Description: Functions for integrating with Ruby tools
+
+" Find the nearest dir contining "app", "db", and "config", and assume it is
+" the root of a Rails app.
+function! ale#ruby#FindRailsRoot(buffer) abort
+    for l:name in ['app', 'config', 'db']
+        let l:dir = fnamemodify(
+        \   ale#path#FindNearestDirectory(a:buffer, l:name),
+        \   ':h:h'
+        \)
+
+        if l:dir !=# '.'
+        \&& isdirectory(l:dir . '/app')
+        \&& isdirectory(l:dir . '/config')
+        \&& isdirectory(l:dir . '/db')
+            return l:dir
+        endif
+    endfor
+
+    return ''
+endfunction