example.cpp: check params and show usage
example.cpp: check params and show usage

example.cpp needs to validate the parameters passed to it and
show a usage message if the parameters are invalid.

ChrisBFX/nanodbc,mcg1969/nanodbc,nanodbc/nanodbc,mcg1969/nanodbc,norsync/nanodbc,nanodbc/nanodbc,norsync/nanodbc,ChrisBFX/nanodbc