make compatible with erlang.mk

[Euen]

[essen]

So I tried that.

Had an issue with bcrypt (ticket open).

Then the next issue is unfortunately not easy to solve because the Cowboy you use is from just about the time when I dropped rebar from Cowboy's Makefile so erlang.mk just runs the Makefile to compile, which then fetches Ranch which requires rebar. Probably works fine for people who have rebar installed, not so much others. This can only be fixed unfortunately by updating the project to a more recent Cowboy. Sorry about that.

Stopped there, don't know if there are more problems.