This is a C version of sparsehash (and also, maybe, densehash) that I
wrote way back when, and served as the inspiration for the C++
version.  The API for the C version is much uglier than the C++,
because of the lack of template support.  I believe the class works,
but I'm not convinced it's really flexible or easy enough to use.

It would be nice to rework this C class to follow the C++ API as
closely as possible (eg have a set_deleted_key() instead of using a
#define like this code does now).  I believe the code compiles and
runs, if anybody is interested in using it now, but it's subject to
major change in the future, as people work on it.

Craig Silverstein
20 March 2005
