new_from_short_name falls back on Software::License::ShortName 

Hello

Previously,```new_from_short_name``` worked using a set of pre-defined short names like GPL-1...

Unfortunately, this means that this method failed when using a short name like ```MIT```.

This patch fixes this behavior: when the passed short name is not known (say ```Foo```), ```new_from_short_name``` tries to load a class like ```Software::License::Foo```. 

I believe that this behavior makes more sense.

All the best