This just updates the proposed 0.19 release to use `secp256k1-jdk` instead
of a more generically defined crypto provider API.
We may want to consider doing this in the 0.18 release or moving
some ECKey definitions into `o.b.base` but this change does not
address either of those proposals.
This updates the document to have 4 diagrams, one for each of the
following releases:
1. 0.16.x (current stable release)
2. 0.17 (according to current plans)
3. 0.18 (according to current plans)
4. 0.19 (this more of a proposal than a plan at this point)
The diagrams have also been enhanced to differentiate between packages
and modules (aka JARs) and to distinguish between "api" and "implementation"
dependencies.
Hopefully this makes things much more clear. We can make further changes
as our plans and implementations change.
