Provided basic image example

Based on jo3w4rd's ticket.
Expose Sphinx project source directory to project info

And provide a helper method for getting paths relative to it.
Extract image nodes from the xml and output

We provide the very basics of support for the \image tag in doxygen
output by reading the name out of the xml and outputting a docutils
image node with the appropriate relative path using the mechanism just
committed.

For ticket #67.
Added image example to specific test page

And changed the documentation a little so that it isn't just an out of
context cut and paste of jo3w4rd's example.
Switch to using Sphinx "absolute" paths for images

The code was getting confused when the .rst file that wanted the image
was not at the top level of the Sphinx project.

Here we change to using the Sphinx "absolute" path concept but
prepending "/" to the relative path from the Sphinx top-level folder.
Without the "/" it thinks that the relative path is from the subfolder
containing the .rst file and so gets confused.
Merge branch 'image-support'