Cane::AbcCheck skips class methods

[dkubb]

I noticed while testing cane that the Cane::AbcCheck#process_ast method does not seem to measure the complexity of class methods.

[xaviershay]

That's a downer :( tbh I pretty much nicked that code verbatim from metric_abc, guess I'll have to get my hands dirty and figure out how it works!