Add `LICENSE` and `DEFAULT_LICENSE` arguments to the `PACKAGE_INFO`
modes of the `install` and `export` commands. If not otherwise
specified, the `LICENSE` will be taken from the project's
`SPDX_LICENSE`, if available.
Add support for specifying CPS's supplemental `description` and
`website` attributes. Add ability to inherit these from the `project()`,
similar to how version information can be inherited.
Modify {export,install}(PACKAGE_INFO) commands to inherit version
information from the current project in situations where it seems
reasonable to do so. Add an option to explicitly request inheritance
from a specific project.
This leverages the recently added project(COMPAT_VERSION).
CPS package metadata involves a fair amount of passing around a
particular set of values, as well as shared argument handling, which is
only going to increase as additional features are added. In order to
reduce code duplication (now and going forward), create a helper class
to handle the shared argument parsing and to serve as a container to
pass metadata values.
