Add PyLS linter (#1097)

* Support PyLS (python language server)
* Replace pyls#GetProjectRoot and add more config types to ale#python#FindProjectRoot

autoload/ale/python.vim

@@ -18,6 +18,8 @@ function! ale#python#FindProjectRootIni(buffer) abort
         \|| filereadable(l:path . '/setup.cfg')
         \|| filereadable(l:path . '/pytest.ini')
         \|| filereadable(l:path . '/tox.ini')
+        \|| filereadable(l:path . '/pycodestyle.cfg')
+        \|| filereadable(l:path . '/flake8.cfg')
             return l:path
         endif
     endfor