Entity renders, recipe and API work.

Splash potion entity now render correctly again.

More work on API, mostly allowing more options and writing lots of
documentation. Might be done unless I think of something I forgot.

Decided to greatly simplify Brewery recipes, removing customization in
favor of simplicity and ease of use. Untested as we still don't have any
recipes in this branch.

Made FluidPotion use the localized name of it's source potion rather
than the unlocalized name.

Fixed bug in MetaItemPotion due to missing set of ().