Merge pull request #1 from gormac/develop

First (test) contribution: Small changes in README.
Add override methods for explicit rounding
Merge pull request #2 from gormac/develop

Added (generated) Specs.txt file to .gitignore.
Added InvalidCurrencyException
Enabled NiGet resstore for build server
Fixed and add test for formatting ExhangeRate
Added RoudingMode to all
ZWK and LVL are made historic,
ZWM added