more eager loading detail in ORM tutorial

[Mike Bayer]

under "Working with Related Objects", take the "eager loading" blurb and make a new section for it "Automatic Eager Loading". put the eagerload() option there, then add another section "Manual Eager Loading" with a basic example of query.join(xx).options(contains_eager(...)). Make sure it links to the more detailed section on contains_eager() in the mapping docs. both eagerload() and contains_eager() should now be considered as equals as there is an appropriateness to each one.

[Mike Bayer]

http://www.sqlalchemy.org/docs/ormtutorial.html#using-join-to-eagerly-load-collections-attributes

[Mike Bayer]

Removing milestone: 0.6.xx (automated comment)