adding allow_null param to nested fields to supress now show children when none exist
Fix bug when a non-dict was marshalled with a fields.List.  Fix just uses the same attribute access style of other field classes.
Document the Nested data type
add another test to verify the behavior
Merge pull request #86 from davidcrawford/fix-list-field

Fix bug when a non-dict was marshalled with a fields.List.
Update fields.rst
Merge pull request #87 from y-p/master

Minor doc fix
add y-p to AUTHORS