Add option to retrieve an address from an output

[eordano]

No description provided.

[yemel]

If no address associated to the script the accessor will throw an error.

I think returning null is a good solution for this scenario, that provides a clean way to check if the output has an address without a try/catch block. The other option is to make it a function and let the error bubble up.

[maraoz]

I would do it via a method, not a property.

[eordano]

Closing, the toAddress method already exists in the script property of the output.

[coveralls]

Coverage increased (+0.0%) to 96.91% when pulling 159b8d8 on eordano:feature/outputAddress into 1f56389 on bitpay:master.