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

where since it considers the current class' ``__table__``, was
sensitive to when it was called.  This is 0.7's behavior also,
but in 0.7 things tended to "work out" within events like
``__mapper_args__()``.  :func:`.has_inherited_table` now only
considers superclasses, so should return the same answer
regarding the current class no matter when it's called
(obviously assuming the state of the superclass).
[ticket:2656]

become an externally usable package but still remains within the main sqlalchemy parent package.
in this system, we use kind of an ugly hack to get the noseplugin imported outside of the
"sqlalchemy" package, while still making it available within sqlalchemy for usage by
third party libraries.

    single-inheritance declarative subclasses,
    with or without using a mixin, can be resolved
    using a new @declared_attr usage described
    in the documentation.  [ticket:2472]

declared on a single-table inheritance subclass
up to the parent class' table, when the parent
class is itself mapped to a join() or select()
statement, directly or via joined inheritane,
and not just a Table.   [ticket:2549]

the vast majority of file lines are spent on documentation, which moves
into package __init__.  The core declarative idea lives in base and
is back down to its originally low size of under 500 lines.  The various
helpers and such move into api.py, and the full span of string lookup
moves into a new module clsregistry.  the rest of declarative only
refers to two functions in clsregistry in three places inside of base.
- [feature] Declarative now maintains a registry
of classes by string name as well as by full
module-qualified name.   Multiple classes with the
same name can now be looked up based on a module-qualified
string within relationship().   Simple class name
lookups where more than one class shares the same
name now raises an informative error message.
[ticket:2338]
- lots of tests to ensure the new weak referencing memory management
is maintained by the new class registry system.   this ticket was
served very well by waiting to do #2526 first, else this would
have needed to be rewritten anyway.