docs target in Makefile is a pointless stub

[mulkieran]

It looks like this:

.PHONY: docs
docs:
        cd doc/_build/html; zip -r ../../../docs *

and inevitably fails. Clearly all it is supposed to do is zip up already existing docs so that these can be released somewhere. What is needed is some doc directory and the necessary infrastructure so that sphinx can be used to generate the API docs automatically. Since we do not expect to release the docs, if this turns out to be very hard to do, the alternative is to remove this useless Makefile target.