[PATCH] Documentation clean ups.

[chrisj at rtems.org]

Hi,

These patches clean up outstanding issues in the documentation:

 - Fix building images in the source directory

 - Provide a text unicode macro for copyright

 - Change --sphinx-verbose to --sphinx-options and add
   --sphinx-nit-pick to make nit-picky checking simpler

 - Allow extra and exclude source files in a build

 - Add a cheetsheet to the README.txt

 - Remove warnings from the User Manual. There are a few in the
   event recorder section I am not sure about and the few remaining
   are ok with one in Overview I cannot figure out.

Chris