cmd: move validation into cmd directories

We can work out the hierarchy more carefully and likely merge these, but
these tools have been moved into cmd/, per Go best practices.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

Makefile

@@ -0,0 +1,22 @@
+
+default: help
+
+help:
+	@echo "Usage: make <target>"
+	@echo
+	@echo " * 'fmt' - format the json with indentation"
+	@echo " * 'validate' - build the validation tool"
+
+fmt:
+	for i in *.json ; do jq --indent 2 -M . "$${i}" > xx && cat xx > "$${i}" && rm xx ; done
+
+.PHONY: validate-examples
+validate-examples: oci-validate-examples
+	./oci-validate-examples < manifest.md
+
+oci-validate-json: validate.go
+	go build ./cmd/oci-validate-json
+
+oci-validate-examples: cmd/oci-validate-examples/main.go
+	go build ./cmd/oci-validate-examples
+