Mark internal Vector constants as private
Use @overload annotation for Hash#fetch docs
Link to #each in Hash#reverse_each docs
Add docstring for Set#sort_by
Removed useless '@api public' annotations from List

As far as I can see, these annotations serve no purpose, since methods with public
visibility are automatically considered part of the "public API" by YARD. If this is
wrong, and there is a good reason to use the annotations, we can add them back.
Added docstrings for most Vector methods