doc fixes

doc fixes

* fixed erroneous use of mapped_column() in m2m relationship Table
* Fill in full imports for some relationship examples that had
  partial imports; examples that have no imports, leave empty for now
* converted joined/single inh mappings to annotated style
* We have a problem with @declared_attr in that the error message
  is wrong if the mapped_column() returned doesnt have a type, and/or
  mapped_column() with @declared_attr doesnt use the annotation
* fix thing where sphinx with undoc-members global setting seems to
  no longer tolerate ":attribute:" entries in autodoc classes, which
  is fine we can document the annotations now
* Fix mapper params in inheritance to be on Mapper
* add missing changelog file for instances remove

Change-Id: I9b70b25a320d8122fade68bc4d1f82f8b72b26f3