- avoid SQLITE_IOERR_BLOCKED with BEGIN EXCLUSIVE 
  Windows at least shows SQLITE_IOERR_BLOCKED after many SQLITE_BUSY, so our
  transaction model with just 'BEGIN' should maybe also provide a 'BEGIN EXCLUSIVE'.
- test execution breaks happily under maximum optimization /Ox (Windows)
- add some basic documentation (doxygen) 
  additional problem: how to generate a namespace prefix in man pages?