Standardize alternate spelling of "class"
I'd like to write `cls` instead of `klass` when creating a generic variable referring to a class object. Both are somewhat standard (mis)spellings across the Python community, but `cls` is a bit more popular, judging from my non-systematic survey.

Sadly, I think `klass` has some awkward cultural undertones, due to its similarity to the word "klan". I understand that's not a global truth, but it leaves a bad taste in my mouth. Making that connection probably wouldn't occur to most folks, but I can't escape it. Happily, we don't have to argue about it as the Pandas project uses both terms and it'd be just as easy to standardize on `cls` instead.

Further, SublimeText's default Python syntax highlighter recognizes `cls` but not `klass`. I'm betting some other editors do the same, changing `cls`'s styling to match `self`.