caltechlibrary/dibs: Release 0.3.1 – Documentation updates & minor bug fixes

This version features updated documentation (including an updated [usage guide](https://caltechlibrary.github.io/dibs/) and updated installation instructions) , and the following minor fixes: * Update the versions of some packages referenced in `requirements.txt`. * Fix issue #66: missing import in `dibs/people.py`. * Fix issue #67: `run-server` should check Python version. The file [CHANGES](CHANGES.md) contains a more complete change log, and includes information about previous releases.DIBS is an implementation of a basic controlled digital lending system