Large Documentation Update

[Gervase Markham]

I've just checked in a massive rearrangement of the Installation 
section, the product of the lion's share of my Saturday :-) It should 
now be a lot easier to understand and shorter.

However, I've undoubtedly thrown out the odd baby with the bathwater, so 
it would be great if people could look it over and see if there are any 
obvious omissions.

Amusingly, this big bit of work has had almost no effect on the 
approximate documentation ToDo list, which remains:

User:
- Request Tracker
- Wildcard matching
- Autolinkification page
- New reporting and charting
- Full text search
- JS-powered comment reply
- Alternative formats of various templates, e.g. CSV, JS, RDF

Admin:
- Time tracking
- Insiders
- requirelogin
- Groups

Cust:
- Term customisation

Contrib:
- The email interface

If you wrote any of these features, please sign up to document them :-)

Gerv