Finish porting tests and documentation to decentralized taxonomy

[Yoric]

Branch decentralized contains a new version of Taxonomy, based on initial brainstorming between @mcav and myself. It now passes its main tests, but a number of doctests have not been ported to the new API yet.

Once work on this repo is done, I'd like to work on

• porting Thinkerbell to Decentralized Taxonomy;
• porting existing Adapters to Decentralized Taxonomy;
• porting the REST API to Decentralized Taxonomy.

Before we can do that, however, we need to finish the work on this repo. @mcav, I don't know if you have some spare cycles at the moment, but I could use the help, both on this repo and on the followup work. I'm leaving on PTO for one week, so my ideal scenario would be one in which you have finished the work on this repo during the time and we can parallelize the rest when I return. If you prefer waiting until I return, I can understand, though.