Add option for displaying long labels for scaled units

[wasnotrice]

For example, display 1.23 Million instead of 1.23M.

This should be an option unit_label with possible values :short and :long defaulting to short. It can then be picked up by the different formatters, in the first version just the console formatter to display long names or short names.

edit (@PragTob) : changed to be a general option and not just for the console

[PragTob]

Moving out of the mile stone as it would make the output considerably longer which could cause problems for the console formatter (as long as it's not fully adaptable to the width) - and it's not exactly needed to release 0.5.0 :)