Docs are a bit clunky

[rkday]

Because the files in this repository generate the whole SIPp site (including docs for previous versions still in use), there are a lot of similar directories (e.g. https://github.com/SIPp/sipp-docs/tree/master/src/documentation/content/xdocs/doc3.2 and https://github.com/SIPp/sipp-docs/tree/master/src/documentation/content/xdocs/doc3.3).

Also, the docs are written in Apache Forrest, which is not very widely used. Long-term, I'd prefer to move to AsciiDoc and host the docs on https://read-the-docs.readthedocs.org/en/latest/getting_started.html. This would also interact with version control, so we could use git tags for building previous versions of the docs, in the same way we mark actual previous releases of the code.