Separate symbols for namespace and vars

By changing the syntax class of `?/` to `"."` (punctuation), Emacs considers the
namespace part and var part of `namespace/var` as two separate symbols.

One improvement is that you can now hippie-expand namespaces and vars
separately. Another is that you can use symbol boundaries to match
namespaces and vars in regexen, with `\\_<` and `\\_>`.

I found the punctuation class to be most fitting, since the Emacs docs say that it is "used in a programming language to separate symbols from one another."