Base library documentation

[Richard Frith-Macdonald]

I have added a subdirectory to the Documentation area of the base 
library for an Objective-C and GNUstep
programming manual.

This contains a texinfo manual (which the makefile system can build into 
info, html, postscript etc) we
have been working on at Brainstorm.

Unfortunately, we ran out of funding for our technical author, so what's 
there is incomplete ... but I
hope that people will find it useful and contribute additions and 
corrections.