Enable third-party online linters

Current tests cover only some functionality, proving it works. But because of python’s dynamic nature, there are bunch of problems, which are commonly missed.

I suggest enabling linters, which are being triggered on each commit or PR additionally to Travis. Personally I’ve used codacy and landscape. I’m satisfied with their features and propose enabling both or one of them.

For example, look at these issues codacy pointed out recently: https://www.codacy.com/app/webknjaz/cherrypy/file/3463172348/issues/source?bid=3283917&fileBranchId=3283917#l1430 There’s misuse of NotImplementedError and missing param while calling method among other errors, which noone mentioned before.

Among other features, there’s an optional possibility to enable adding comments upon checks finish to PRs/commits, which could be very useful.

/cc: @jaraco

[jaraco]

It’s also possible now to run tox -e linter to run the linters.

[webknjaz]

Codacy allows disabling some of errors if needed. Regarding tests @ Travis, there’s this cool utility tool called pre-commit which I use for a while. It lets users nicely organize common checks and can be added locally as pre-commit or pre-push script, running preconfigured hooks on changed files only. Also it can be used as one of CI checks.

For now, I suggest enabling just codacy to see what we’ll get 😃