Task: Have checksums be generated for files released on Github

When releasing the generated tars on github, we should release a
checksum file alongside it. Have a dist target for the Makefile that
will tar up the actionpacks and create a checksum file as well for them

Change-Id: I17a0c562a698f1cd5d6914cc9b23dbfd39210b6a

Makefile

@@ -2,7 +2,7 @@
 # Use of this source code is governed by the Apache License 2.0
 # that can be found in the COPYING file.
 
-.PHONY: actionpacks lint
+.PHONY: actionpacks dist lint
 
 lint:
 	flake8
@@ -19,4 +19,7 @@ actionpacks:
 actionpacks-mac:
 	mkdir -p gen
 	find . -mindepth 1 -maxdepth 1 -name "*action-pack" -type d -execdir tar --disable-copyfile -cf {}.tar {} \;
-	mv *.tar gen
+	mv *.tar gen
+
+dist: actionpacks
+	cd gen && sha256sum * > CHECKSUMS.sha256