Metadata parameters

[KatamariJr]

Adds some features to make it a little bit easier to add metadata to a request per #7 . Values need to be base64 encoded before they are passed as parameters, but its a start.

Adds two new params: -n : automatically adds the "name" metadata value as it was doing already -m : accepts a list of key-value pairs, and passes them along into the Upload-Metadata header. Invoker must take care of base64 encoding the values themselves beforehand.

[KatamariJr]

I agree with all those points you made! I dont know enough about shell to know how to split a list of params into an associative array like that, but if you point me in the right direction or give an example, I could implement it!