Revised new macros after discussion with Guido: Always use full names of

Revised new macros after discussion with Guido:  Always use full names of
semantic concepts.

Added two new ones (not discussed with Guido:

\constant{}:  Markup for constants defined in Python modules.

\cfunction{}:  Markup for C functions; these should probably be distinguished
	by font, but are not at this time (since they're typically \code{} at
	this point).