Fully automate the generation of the reference section

[fiiiu]

Right now, the reference section is generated in a partially automated form, using gen-docs for zos-cli, and solidity-docgen for zos-lib, and then pruning the corresponding outcomes and merging them manually.

We need to provide a script to do all of this, plus maybe the deployment, in a fully automated way. This will likely be most easily achieved by tweaking gen-docs (zeppelinos/zos-cli#143) and solidity-docgen to conform to the required pattern, and then simply merge with a script.

This pertains the generation of the .md files in the docs/docs/ folder, as well as the sidebars.json file. Finally, this is the first step towards having automated versioning for the docs (#78).