Add a Makefile

This is a very simple Makefile that just passes through to the current hack/*
scripts.  Only "make", "make test", and "make clean" are supported for now.

@filbranden 
Looks to me that this change is unrelated to adding a Makefile... Separate commit? I like tiny commits on git because then if there's a bug it's easy to revert... Not so if they're spawning unrelated changes.