Add intro to writing a plugin in the new (unnnamed) framework.

[ethanfrey]

The code in here compiles and is tested for a simple counter app:https://github.com/tendermint/basecoin/tree/unstable/docs/guide/counter

This whole plugin intro is deprecated:
https://github.com/tendermint/basecoin/blob/unstable/docs/guide/basecoin-plugins.md

Much more info is here:
https://github.com/tendermint/basecoin/tree/unstable/docs/quark

Maybe you can try to make an explanation of how to build the counter module, if you can understand it from what is there. If not, ask us how to do it, and then explain it in your words.

[ethanfrey]

There is also PR #211 which you can look at and see the whole process of making a new module and app in a few commits.

Maybe that is an even simpler intro...

[ebuchman]

stale. we need docs