- to account for query._attributes/context.attributes, just pass
the attributes dict directly to the PathRegistry methods

- went through examples/ and cleaned out excess list() calls

to work before the object is initialized, so
that Sphinx builds with recent Sphinx versions
can read them.

added, which proxies down to the ``.info`` attribute on either
the :class:`.schema.Column` object if directly present, or
the :class:`.MapperProperty` otherwise.  The full behavior
is documented and ensured by tests to remain stable.
[ticket:2675]

construct after it's been constructed already.  This is not
a pattern for normal use but we like to change the setting
for demonstration purposes in tutorials.

associated with the ORM or its extensions can be retrieved.
This fulfills the common request of being able to inspect
all :class:`.QueryableAttribute` descriptors in addition to
extension types such as :class:`.hybrid_property` and
:class:`.AssociationProxy`.  See :attr:`.Mapper.all_orm_descriptors`.

- paths now store Mapper + MapperProperty now instead of string key,
so that the parent mapper for the property is known, supports same-named
properties on multiple subclasses
- the Mapper within the path is now always relevant to the property
to the right of it.  PathRegistry does the translation now, instead
of having all the outside users of PathRegistry worry about it,
to produce a path that is much more consistent.  Paths are now
consistent with mappings in all cases.  Special logic to get at
"with_polymorphic" structures and such added also.
- AliasedClass now has two modes, "use_mapper_path" and regular;
"use_mapper_path" is for all those situations where we put an AliasedClass
in for a plain class internally, and want it to "path" with the
plain mapper.
- The AliasedInsp is now the first class "entity" for an AliasedClass,
and is passed around internally and used as attr._parententity
and such.  it is the AliasedClass analogue for Mapper.