implementing TopicBasedHelp

[Matthew East]

I've started a separate branch for some experimentation for implementing
the topic-based-help specification, since I think that it requires some
fairly severe changes to the layout of the repository.

You can grab it here:
https://docteam.ubuntu.com/repos/branches/topic-based-help/

For now, the branch only includes Ubuntu documents. When we've figured out
what will ultimately be the structure we adopt, we can merge it back into
trunk and apply it to the kubuntu/edubuntu/xubuntu directories as
necessary.

Some notes.

First, inter-linking. I think the best way to do this is simply to use
normal <link> or <ulink> tags to link to another document. Since this
isn't easy to do with the current translation structure we use
(documentname/language/documentname.xml), I think we will have to switch
to (language/documentname/documentname.xml). This means that relevant
links should work for all languages without having to do any tweaking or
substitution or anything.

A number of what used to be chapters of the desktopguide are likely to
become single documents. I've fixed up a couple of these to show how that
might work (add-applications and games), and the others are not yet fixed
up. I've made a note of which ones aren't working in the appropriate
directory.

Does anyone have any comments on this sort of directory structure? It's a
bit difficult to predict what problems it might cause, so I'd love some
feedback.

Matt