Make mjolnir.useCircuitBreakers=true by default

The config value was originally a failsafe in case we found problems with
them, and that's the only reason it really still exists. Unlikely that
it'll ever need to be false, so defaulting it to something more sensible.
Add support for Hudl.Mjolnir.Attributes package
Deprecate VoidResult
Minor comment for clarification
Merge remote-tracking branch 'origin/DefaultCircuitBreakersEnabled' into IntegrateAttributesPackage
Merge pull request #29 from hudl/IntegrateAttributesPackage

Add support for Hudl.Mjolnir.Attributes package