In-memory issuing: open PRs

First of all thanks for all your great hard work, and for sharing it with the world!

I’ve been following the project for some time and one of the biggest points of improvements I saw in the cert-tools and cert-issuer repos was the heavy reliance on the filesystem for the issuing process: there’s several config files, intermediate json files being created for unsigned certs, image files and finally another set of json files for the final, signed certs. This creates issues like race conditions when trying to use these repos from an application. So I went ahead and suggested some changes to achieve in-memory issuing (so the code can be used more like a library and less like an application), with tests to show how the code can be used and how it still produces fully compliant blockcerts. The suggestions were split into four PRs to make it easier to review:

I was hoping to get the discussion going here on what can be done from my end to help getting these merged?
Thanks!