this would cause LazyLoader to be initialized twice per property.

for memoization on a class that uses slots.
- apply many more __slots__.  mem use for nova now at 46% savings

size of the many per-column objects we're hitting, but somehow the overall memory is
hardly being reduced at all in initial testing

- prop.compare() isn't needed; replace with prop._with_parent()
for relationships
- update docs in orm/interfaces

instances(), using a named tuple it can assign to directly.  this way
we never have to worry about that structure changing anymore, though
we are still having it append (key, fn) which is kind of awkward.
- inline _populators() into instance(), it's a little verbose but
saves an fn call

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

:class:`.InspectionAttr`, where in addition to being available
on all :class:`.MapperProperty` objects, it is also now available
on hybrid properties, association proxies, when accessed via
:attr:`.Mapper.all_orm_descriptors`.
fixes #2971