Make require-r compatible with the full require spec

[daslu]

At the moment, require-r supports only basic syntax analogous to Clojure's require and Libpython-clj's require-python.

We wish it to become fully compatible with require-like syntax.

[genmeblog]

Just to mark: :refer :all is low hanging fruit.

[genmeblog]

:refer :all is done
:as is done (but should be corrected to use alias instead of creating another namespace)
:as-alias - not needed I think
:exclude, :only, :rename - to consider