Add support for Azure Copy Blob

Presently lacks support for CopyBlobOptions.  API reference:

http://msdn.microsoft.com/en-us/library/dd894037.aspx
We're preferring `Optional` to an overload here? Is this a pattern we use elsewhere? Otherwise, how about two methods:
```
copyBlob(URI copySource, String toContainer, String toName);
copyBlob(URI copySource, String toContainer, String toName, CopyBlobOptions options);
```
or
```
copyBlob(URI copySource, String toContainer, String toName, CopyBlobOptions... options);
```
?