Proposal for adding an example "expanded" data type to contrib

Hello,

Expanded data types (types that have a different in-memory working
representation than on disk) are pretty essential to a couple of projects
that I work on, and while the prose documentation is great at explaining
the rationale and technical overview, there isn't a complete,
self-contained, simple example of an expanded data type. Readers of the
documentation are encouraged to study the array type code.

To wrap my own head around it, and to have a sort of template to quickly
spin up future expanded types, I wrote a simple extension that does nothing
useful other than show how to create and handle an expanded type.

https://github.com/michelp/pgexpanded

I posted this last week to psql-general, and Pavel Stehule suggested it
would be a good candidate for inclusion in the contrib collection and that
I write this proposal to suggest the extension get into the next commit
fest.

I have not contributed to the core of postgres in the past so please excuse
my ignorance on the process. Does anyone have any comments or objections
to me pushing this process further along?

-Michel