Adds support for Index.Meta.index_name to specify the index name. Fixes #23
Implements #22, using Model.Meta attributes to define read/write capacity units.
Correctly handle __null=True and __null=False filters for Model.scan, fixes #24
Correctly set NULL and NOT_NULL in query scan operations. Fixes #24
Release notes for 1.3.0
Merge branch 'devel'

* devel:
  Correctly set NULL and NOT_NULL in query scan operations. Fixes #24
  Correctly handle __null=True and __null=False filters for Model.scan, fixes #24
  Implements #22, using Model.Meta attributes to define read/write capacity units.
  Adds support for Index.Meta.index_name to specify the index name. Fixes #23
v1.3.0