Makefile: add release rule.
Makefile: add release rule.

The release rule create a repository under ./releases/$(RELEASE) directory:
$ make release && find releases/
releases/
releases/0.1.1
releases/0.1.1/mpkg_0.1.1.tgz
releases/0.1.1/mpkg-tools_0.1.1.tgz
releases/0.1.1/Index

Signed-off-by: Gaël PORTAY <1666f60cfa201a60b0ea694168a0b6932673170a@gmail.com>

gazoo74/mpkg,gazoo74/mpkg