Add pylint formatter

This customizes the output format of pylint in order to use the same
pep8 parser

ale_linters/python/pylint.vim

@@ -0,0 +1,9 @@
+" Author: keith <k@keith.so>
+" Description: pylint for python files
+
+call ale#linter#Define('python', {
+\   'name': 'pylint',
+\   'executable': 'pylint',
+\   'command': g:ale#util#stdin_wrapper . ' .py pylint --output-format text --msg-template="{path}:{line}:{column}: {msg_id} {msg}" --reports n',
+\   'callback': 'ale#handlers#HandlePEP8Format',
+\})