DBDoc schema documentation generator

Documentation regarding the descriptions file is split
between the hope page, and a few lines within the
code. The command line options to use the
descriptions file and 'tables' option are not
documentated clearly.

"A java-style properties file can optionally be used
to add human-readable descriptions of such schema
elements as tables, columns and indexes."

lib/dbdoc/dbdoc.py
# Valid property file entries are:
# schema.name
# schema.notes
# table.<tablename>.shortdesc
# table.<tablename>.notes
# table.<tablename>.column.<columnname>.shortdesc
# table.<tablename>.index.<indexname>.shortdesc