Massively improve documentation

It is with joy that I make this pull request for possibly the longest lived card in the Riff-Raff backlog.

All of the docs have been overhauled as a result of presenting a talk on Riff-Raff to the Guardian Dig Dev department. The primary aim of the work has been to document both magenta and riff-raff more comprehensibly. However this pull request isn't just a bunch of markdown updates - it also has under the hood changes to make it possible to generate documentation directly from the deployment types.

The main changes included here are:

 - New and updated markdown files that document magenta and riff-raff
 - Addition of breadcrumbs and other navigation within the documentation pages
 - Converting deployment types from classes to companion objects and making it possible to look the up at runtime
 - Changing deployment type parameters to have an abstracted extraction system for getting the parameters from the deploy.json
 - Adding documentation fields to both `DeploymentType` and `Param` and populating the field in all implementations and instances