simple but unusual system allows for a dramatic savings in Python
overhead for the construction and processing of orm :class:`.Query`
objects, from query construction up through rendering of a string
SQL statement.
fixes #3054

didn't match.  use straight memoized_props here for now, add a perf test to check it

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

    inheriting mappers to be GC'ed when the
    class itself is deferenced.  The mapper
    must not have its own table (i.e.
    single table inh only) without polymorphic
    attributes in place.
    This allows for the use case of
    creating a temporary subclass of a declarative
    mapped class, with no table or mapping
    directives of its own, to be garbage collected
    when dereferenced by a unit test.
    [ticket:2526]

now accepts aliased() class constructs as well
as with_polymorphic constructs, and works with
query.join(), any(), has(), and also
eager loaders subqueryload(), joinedload(),
contains_eager()
[ticket:2438] [ticket:1106]
- a rewrite of the query path system to use an
object based approach for more succinct usage.  the system
has been designed carefully to not add an excessive method overhead.
- [feature] select() features a correlate_except()
method, auto correlates all selectables except those
passed.   Is needed here for the updated any()/has()
functionality.
- remove some old cruft from LoaderStrategy, init(),debug_callable()
- use a namedtuple for _extended_entity_info.  This method should
become standard within the orm internals
- some tweaks to the memory profile tests, number of runs can
be customized to work around pysqlite's very annoying behavior
- try to simplify PropertyOption._get_paths(), rename to _process_paths(),
returns a single list now.  overall works more completely as was needed
for of_type() functionality