1.4.0

Improved DynamoDbItem exceptions.

1.3.2 - clean up handling of expression attribute names/values

v1.3.2

1.3.2 - under the hood improvements to expression attribute approach

Fix bug in `add_variables_to_expression`

1.3.1

Merge pull request #2 from xoeye/bug/fix-issue-with-adding-variables-…