Update readthedocs to weave 0.12

[ethanfrey]

https://weave.readthedocs.io/en/latest/index.html is generated from https://github.com/iov-one/weave/tree/master/docs (always master).

The information there is mostly correct, but somewhat out of date. Please go through, try all commands, and update them to work with weave 0.12. Then add a big note at the top that this works with weave 0.12 (so we see a problem when weave is at 0.14 and we still haven't updated them).

You can gladly make some changes, like using bcpd instead of mycoin as the demo app. You may want to update the Makefile as well, so it is easier to install.

This is not about improving the docs, but rather updating them.

All code for the javascript/typescript client (iov-core) can be removed and replaced by a link to the docs on that repo, which are more guaranteed to be kept up to date. This means mycoin tutorial can be removed, and requirements/installation moved to deployment.