Create a license guideline document for the project. This pulls together all the
disparate docs into one location.
Also, introduce a new policy to allow SPDX identifiers to completely specify a
license and specify the mechanics of how to construe the license for such files.
Changes of note:
o Our model license and the SPDX model license have slightly different text. This switches us to the SPDX text.
o This also switches our default preference to using the detached license with the SPDX keyword.