Libconsensus completion plan document (with pictures)

Hello, since trying to encapsulate consensus code without exposing anything else (see my post from january https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2016-January/012235.html ) wasn't succesful in getting review, I decided to turn "phase 2" into "expose verifyHeader" again. I was previously starting the document with pictures but since things we're changing and the pictures were already deprecated, I decided to wait after segwit was merged and include those changes in the pictures too. This time I created a repository so that people can look at it, even if it's less advanced than previous versions have been:

https://github.com/jtimon/consensus-doc

Here's a branch with the resulting images, latex file and pdf:

https://github.com/jtimon/consensus-doc/tree/generated

And here's the pdf:

https://github.com/jtimon/consensus-doc/blob/generated/libconsensus.pdf

Any questions or comments are welcomed. If some of the images are wanted for some other more general documentation or you want me to create a specific diagram to document Bitcoin Core I'm happy to do so as well.

Note that some phases can be done in different order or in parallel (ie phase 3 and phase 4 could happen before phase 2, although I strongly doubt it because phase 2 is the simplest to review and I've been harassing different people to do it for a while with little success [thanks to those who reviewed it and gave feedback] ).

An implementation of phase 2 (expose verifyHeader()) can be seen in https://github.com/bitcoin/bitcoin/pull/8493