WIP Better pylint message equivalence

Pylint has 6 error categories, and currently ALE maps them to two: Error and Warning (all codes that are not errors are classified as warnings)

This patch proposes the following mapping: Error => ALEError Warning => ALEWarning Convention => ALEStyleWarning Refactor => ALEInfo

Where are the tests? Have you added tests? Have you updated the tests? Read the comment above and the documentation referenced in it first. Write tests!

Seriously, read :help ale-dev and write tests.

Please fix the whitespace on the blank line (line 96) so the tests can run.

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests. If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.