Additional loud noises

This release adds support for:

• date-time and int-or-string string formats #155, thanks @jcdlbs
• Objects with no properties (implicitly anything) and associated additionalProperties support #156, thanks @jcdlbs
• hato client in martian-test #158, thanks @bombaywalla
• cljs-http-promise in martian-test #159

This release fixes:

• The cljs-http stub responder in martian-test now returns a proper asynchronous contex #159

This release improves:

• The martian-test code example in the README #152, thanks @rkirchofer
• The respond-with (replacing respond-with-constant) function in martian-test now accepts functions as well as values #159