- major refactoring/inlining to loader.instances(), though not really

- major refactoring/inlining to loader.instances(), though not really
any speed improvements :(.   code is in a much better place to be run into
C, however
- The ``proc()`` callable passed to the ``create_row_processor()``
method of custom :class:`.Bundle` classes now accepts only a single
"row" argument.
- Deprecated event hooks removed:  ``populate_instance``,
``create_instance``, ``translate_row``, ``append_result``
- the getter() idea is somewhat restored; see ref #3175