Keep bools and reject odd number of args

[zmaril]

• A simple assert makes sure that the number of kv's passed to make-args is always even.
• Boolean values, specifically falses, were getting lost due to the use of a bare or. By switching to using dv in the get-in instead, the code is both simpler and more correct.

[zmaril]

Hmm it looks like the number of args doesn't always have to be even? Happy to revert that part.

(make new-webserver config {:port [:http-server :port]})