more consistent use/description of predicate in documentation, ie in all()

I found the documentation for all and any confusing because I didn't realize predicate was a function.  I modeled the language on the existing skipchars documentation.

I assume this shouldn't go straight to master, but I don't know where it should go and figure someone will change it.

I'm still getting used to git/github so I think I messed something up with lots of commits being involved, but it only actually changes one file.