Add info about K being position dependent to the docs/comments

[kergoth]

I'd suggest adding info to the header documentation in the ftplugin, about the position-dependent behavior of K. Specifically, that it doesn't cross '.' boundaries to the right, only to the left. I can see why you did it that way, and I can see the value, but it wasn't what I was expecting K to do, as it doesn't normally act that way. I didn't discover that I wasn't going to have to remap K or manually use pW until I read the definition of ExpandModulePath :).

Thanks. Quite liking the ftplugin so far.