Initial submission of dbaugment tool with support for audit columns.

 * docs/{augmentdb, augobjects, cfgobjects, dbaugment, predefaug}.rst:
   Document sources for new tool and related objects.
 * docs/index.rst: Add new tool and objects to TOC.
 * pyrseas/augment/{__init__, audit, column, function, schema, table,
   trigger}.py: Sources for new augmenter objects.
 * pyrseas/augmentdb.py: The new tool itself.
 * pyrseas/dbaugment.py: Derived class to implement augmenter databases.
 * pyrseas/testutils.py: New test class for augmenter.
 * tests/augment/test_audit.py: Tests for audit columns support.