CurrencySystem

Hi all,

I wrote the following blog to appeal to those interested in use cases that
require CurrencySystem to step up and log their use cases:

https://medium.com/@ahopebailie/currencysystem-is-at-risk-d29aebafdd38

@editors: I have reopened issue 490 as this is the issue referenced in the
spec but have recommended new issues are raised if they are a new use cases
to keep threads manageable.

@marcos/mike: I also requested people provide test cases for their use
case. Any help you can provide on this would be very helpful.

Adrian