Implement batch actions.

[danielgtaylor]

This change implements batch actions on collections:

s3.Bucket('boto3').objects.delete()

It does the following:

• Create a CollectionFactory class to generate subclasses of
  CollectionManager and ResourceCollection.
• Update the ResourceFactory to use the new CollectionFactory.
• Add a public pages() method to collections. This returns entire
  pages of resource instances and it used by __iter__ as well.
• Add batch actions as methods via the new CollectionFactory.
• Add a BatchAction subclass of Action which does the following:
  1. Get a page of results from the collection's operation
  2. Build parameters for the batch action operation
  3. Call the batch action operation
  4. Repeat until no more pages
• Makes some previously public members private on Action as these
  should never have been public.
• Update documentation to include collection classes.
• Fix a couple minor documentation issues.
• Add tests to cover the new functionality.

cc @jamesls, @kyleknap

[coveralls]

Coverage decreased (-0.0%) when pulling cfa443437b6012d341518a25a321bf79847fc796 on batch-actions into ab3b951 on develop.

[kyleknap]

Looks good. 🚢 You may want to add a test that does a Collection.page_size().pages() to ensure that you never run into issues for that case. I would picture a test similar to the test you did for limit()

[danielgtaylor]

@kyleknap I've rebased onto the latest develop and added a test to ensure page_size is adhered to when calling .pages().

[coveralls]

Coverage decreased (-0.0%) when pulling 30463ab on batch-actions into 8ea77b9 on develop.

[kyleknap]

Thanks! 🚢