Address: Added toObject method and changed toJSON to return a string
Block: Added toObject method and changed toJSON to return a string
HDKeys: Added toObject method and changed toJSON to return a string
Keys: Added toObject method and changed toJSON to return a string
URI/Unit: Added toObject method and changed toJSON to return a string
Transaction: Added toObject method and changed toJSON to return a string
BN: Remove toJSON and fromJSON methods from BN, as they are equivalent to toString and fromString
Contributing: Added G7 "Standard Methods"
Unit: Fixed bug, stringified toJSON output
Merge pull request #736 from braydonf/feature/to-object

Added `toObject` methods to return an `object` and modified `toJSON` to return a `string`. Closes #732