Checkpoint. Start with some tests.
Account for in-flight messages.
Use priority queue so that we can simulate returned messages.
Add tests for deleteMessage.
Add class javadoc and fill out some other stubs.
Add some finals...
Merge branch 'master' into rayortigas

* master:
  Tick to 1.3.3.
Tick to 1.3.4-SNAPSHOT.
Don't bother trying to support multiple threads.
Fix receiveMessage to match spec (1 by default, at most 10 if requested).
Implement receiving of messages but only with requested attributes and message attributes.
Merge pull request #4 from rayortigas/rayortigas

Add SQS stub.