documentation installation tree

[nicola]

Hi everyone,

I added installation/uninstallation to documentation.make, then used the
new stuff to install the core documentation.

I had to decide where to put things in, and, quite inspired by

http://www.made-it.com/GNUstep/Administrator/tree-sys.html

:-) I organized things as follows:

System/Documentation/Developer/CodingStandards/
System/Documentation/Developer/Base/Manual/
System/Documentation/Developer/Base/Reference/
System/Documentation/Developer/Base/ReleaseNotes/0.6.6/
System/Documentation/Developer/Gui/Manual/
System/Documentation/Developer/Gui/Reference/
System/Documentation/Developer/Gui/ReleaseNotes/0.6.6/
System/Documentation/Developer/Xgps/ReleaseNotes/0.6.6/
System/Documentation/Developer/Xdps/ReleaseNotes/0.6.6/

I would be happy to discuss the question and of course improve on this
arrangement if someone has some objections.