Add subset type to subsets in API

[UltraGodAzgorath]

Hey guys.

I would like to suggest changing "~ Subset ~" in the API to the specific multiset type the game is for.

~ Subset ~ (If a subset doesn't have multiset enabled yet.)
~ Bonus Subset ~
~ Specialty Subset ~
~ Exclusive Subset ~

With this change, players can see the type of subset in the game name on the gamelist pages, they'll be able to see when games have their subset type changed and I can tell my DAT builder to automatically skip adding ~ Bonus Subset ~ games to the RA DATs.