3.1.0

Extract new ReadablePayloadInterface and WritablePayloadInterface from
PayloadInterface, then compose PayloadInterface from them. Existing
implementions of PayloadInterface should continue to work, making this a
backwards-compatible change.

3.0.0

First stable release.

3.0.0-beta1

This release adds a PayloadStatus class of constants that is implementation-independent.

3.0.0-alpha1

First 3.x alpha release.