Require a string value to instantiate Binary DynamoDB type

Prevents incorrect usage which results in potentially confusing errors.
Fixes #1956.
Fixed to no longer duplicate issues in release notes.
Add support for arbitrary dict inputs to MWS calls
PEP8
Add unit tests for instantiating the DynamoDB Binary type.
Merge pull request #1963 from danielgtaylor/ddb-binary

Require a string value to instantiate Binary DynamoDB type. Fixes #1963, #1956.
Merge branch 'rn-issue-dupe-fix' into develop
Fixes #1965