Teach release notes script to take an optional prefix parameter
Teach release notes script to take an optional prefix parameter

With this parameter and the help of a convention we can now produce
release notes for projects spread across multiple repositories.

In the "main" project repository we just invoke the script as normal
(without parameters) and it uses "git describe" to find the last tag,
the previous tag, and emit the differences between them.

In the secondary repositories we pass a "tag prefix" which we use to
locate the tags corresponding to the release of the "main" project; in
other words this depends on a convention in which we create tags in
the secondary repositories which have a unique prefix which identifies
the main project.

Signed-off-by: Wincent Colaiuta <c76ac2e9cd86441713c7dfae92c451f3e6d17fdc@wincent.com>

wincent/buildtools,wincent/buildtools,wincent/buildtools