Adding a common utility so prosper projects can have sane and up-to-date version information. Also in this release, we have added handy [readthedocs](http://prospercommon.readthedocs.io/en/latest/index.html) support for documentation!
* Added `prosper_version` modules for version finding. TYVM [ccpgames/setuphelpers](https://github.com/ccpgames/setuphelpers)
* Added `sphinx` docs with `napoleon` autodoc support. See our docs at [readthedocs.io](http://prospercommon.readthedocs.io/en/latest/index.html)
* Requirements now floating/latest: Please be sure to tag expected version in dependent projects
* Touched up `README.rst` to reflect style of other Prosper projects
* Removed unused functions from `prosper_utilities`
* Added custom exceptions support
* Improved webhook-message-fail case
* Updated Travis-CI test coverage to Python 3.6
* Updated test names to match style in other Prosper projects
* Added `quiettest` option for testing w/o spamming webhooks