Fixup cmd build

When first trying to get doozer running to play around with it I got really confused on how to build the doozer client from the git directory. This tries to simplify that process and make it follow go norms by moving that code into the src/ directory.

Also it adds a convenience make target so that people can quickly get started from git.

I can provide a follow on PR that creates a symlink from cmd/ to src/util/ so that the old `go get` instructions still work.