Added support to the XML builder for XML namespaces and attributes.
Added support for parsing XML elements with the encoding="base64" attribute.
Added support for parsing XML elements with varied attributes (like xmlns).
Added unit tests for serializing and parsing complex XML payloads for S3 operations.
Removed the fixed encoding from AWS.util.base64.decode and added some tests to exersize utf8 encoding/decoding.
Removed the test/unit folder (flattened into test/).