Outline a roadmap

[pnorman]

There should be a roadmap for plans for the schema. I suggest the following as a start

1. Continue to work on the definition of layers to make it clearer what is included and how to interpret it, as well as improve the formatting to be more consistent and easier to read
2. Define a versioning policy
3. Make backwards compatible changes for 1.1 like adding more name languages

I don't want to plan too far ahead because we don't know what we should be doing until we get more users.

Additionally, I think we should be freer about changes to the 1.0 spec than we would want to be for the 1.1 and 2.0 specs. This is the first release, so there's more to fix as we learn from publishing it.