Git commit 644ee5991a4a55e2391c4c43483b878e87a95bc0.
Restructured chapter filenames to reflect the DocBook "part" they belong to.
Most sections are now completed. The add-on docs are actually quite complete now. The advanced add-on chapter is really all that remains, with treatment of Roo internals.
I deleted the "getting started developing" section that was based on the readme.txt. It's more likely we'll keep readme.txt up to date, and it's what someone doing a checkout would want to consult with. I also moved the treatment of how to install an add-on to an earlier section aimed at end users, rather than leaving it in an add-on development section. Other structural changes of that nature were also performed, plus new content written.