further 2.2 resubmission work, 42.3 work + images

I have continued with the 2.2 resubmission by adding more explicit
information about how different packages improve system performance.

I also created the syntax for custom markdown includes (%% include
path/to/file.md %%) and fixed an issue with the header regex business in
index.php. I started the User Documentation for 42.3 and realised I had
mistaken Tech Docs for User Docs.

2.3 changed too for some reason. Look at the diff; I've forgotten what I
changed.