Multiple packages from single repository.

Something that has come up a couple of times is the ability to have one package to export multiple packages at build time.

Say that we have a ocean package that generates an ocean simulation library, Houdini deformer, Maya Deformer, Arnold Shader etc...

**I would like to be able to generate packages like:**
- ocean_core-1.0.0
- ocean_deformer_houdini-1.0.0
- ocean_deformer_maya-1.0.0
- ocean_shader_arnold-1.0.0
The deformers and shaders would have dependency on ocean_core.

**Or one package:**
- ocean-1.0.0
This one would partially include configurations based of the rest of the resolved packages.
i.e. `rez-env maya ocean` Would not set configurations for Houdini.

I don't know if something like this is already supported.

/Fredrik

No files, tests, or entry points are mentioned. Start by checking the existing package-definition and build documentation for support for multiple outputs from one repository. Done should include generating the separate ocean_core, Houdini, Maya, and Arnold packages with dependencies, or the combined package with host-specific configuration behavior.

Written by the indexing model from the issue text.