make check_length work for projects other than Launchpad

[Adi Roiban]

Right now, the formatchecker has a /lib/lp hardcoded as the condition for checking a non-PEP line length .

In case other projects are using a non-PEP line length it would be nice if pocket-lint will allow some soft of easy customization.

I have attached a branch with adds a degree of customization. It uses a dedicated method for filtering line length checks and returning the length of the line.

Users can path BaseChecker and PythonChecker to change the behavior of check_length.

Another approach would be to add an argument to UniversalChecker and pass the method as argument, but for me, the manual patching looks good enough.

[Curtis Hovey (sinzui)]

You can now specify the max length using --max-length or -m command line args. The default max length is 80. To verify that a text file conforms to email line-length, you can run this:
    pocketlint -m 72
To verify Lp's rules set the max-length to 78:
        pocketlint -m 72