Update building stuff

- Add a Makefile with common targets (binary, test, validate, ..)
- Use docker to build it (isolated)

And update circleci to work with the new Makefile..

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

script/generate

@@ -0,0 +1,4 @@
+#!/bin/bash
+set -e
+
+go generate