0.3.1 Release Candidate 1

UPPERCASE WARNING: THIS IS A RELEASE CANDIDATE AND IS NOT INTENDED FOR DOWNSTREAM USE.

This source is a candidate for release version 0.3.1. Please see #391 for testing instructions and where to leave your feedback.

Compared to the previous release, this candidate includes

• #362 Update MongoDB driver to 3.0.3
• #381 Work around HDRHistogram initialization bug
• #359 Shutdown the client as soon as all workers are complete
• #239 Print estimated time remaining in status thread

Additionally, it includes some project internals (#366, #389, #393)