BETA RELEASE: v3.0.0 beta 2

[Warren Young]

Since the last version, it's mostly been bug fixes, documentation 
improvements, and testing.  The only "new features" of note are:

- Renamed custom* to ssqls*.  There's a custom.h file included with the 
tarball for compatibility with existing code, but this will go away 
eventually, probably in v3.1.

- Added examples/cpool.cpp, to test ConnectionPool in a threaded 
program.  It works with both Windows and POSIX threads.

Based on the fairly low volume of comments, I'm not sure if there will 
be another beta.  Maybe just a release candidate and be done.  The most 
aggressive schedule would have a final release in about a week.