include the start-line directive here so that we dont get warnings
for the headers in the included files
- add a new sphinx extension "viewsource".  takes advantage of part of the viewcode extension
to allow ad-hoc display of the source of any file, as well as a "directory listing" structure.
- reorganize examples/ to take advantage of new extension.  in particular, keep moving all
the descriptive text for files etc. into module docstrings, taking more advantage of
self-documentation.