Update installation guide for Debian (derivatives)

I don't really know how this happened, but the guide on the web page
(stored in a .html on gh-pages branch) is way ahead of this .rst file.
Have we updated the documentation just in the HTML and not in the source
file???

Weird. Anyway, I've backported the changes from the .html file to this
.rst file so they are now in sync again.
Add INSTALL file and rename other INSTALL file

Part of #448.
Rename getting-started guide

It's really installation on a Debian-like system.

Part of #448.
Removed some old API doc

This was a design document for the API. Now that the API implements all
those features and has integrated docstrings, I've removed this older
document.
Add doc stuff... need to sort stuff out
fooo
foo
Use RST style links

Also add a Makefile to render output into .html!
Merge branch 'update-install-docs'