"Three Cs": Further development of PlanetMath/Planetary

[holtzermann17]

Marking this ticket as "ongoing" - it provides a coherent framework for analysis.

The future of PlanetMath can be considered in terms of the following 3+2 dimensions: Community, Catalog, Content, as well as Software and Organization. All of these aspects could use further development.

Software ends up creating the context where we work, and the actions
that are available within this context.

Community is important since there have to be people to engage in
order for this kind of stuff to grow.

Organization features can help develop PlanetMath through both
“inreach” and “outreach” aspects, noting that we tend to get different
kinds of content and different kinds of quality judgements through these
different efforts.

A richer catalog of mathematical content would show what links to
what, not just locally, but in a cross-cutting sense (a PlanetMath Cross
Index to mathematical literature, expanding on the APM-$\Xi$ idea).

The content of PlanetMath defines (or constrains) the topics of
interest, the kinds of things you can do, and the ways of thinking about
them.