Add Buffy the Vampire Slayer: Wrath of the Darkhul King

[joshbarrass]

Adding the dialogue scenes from the BtVS: Wrath of the Darkhul King GBA game. Everything's dumped pretty much as it comes from the original game, which means (for most characters) the backgrounds and character sprites are separate. I wanted to keep it that way to give as much freedom as possible; this way, you can put the character sprites on a different background (although for most of them it'll look pretty terrible because of the huge blob in the centre).

Nametags are also handled independently of sprite/background. This is relevant for one case, pretty much: the gentlemen background doesn't feature any character sprite, but features a different character talking about what we see (see the gentlemen test case).

Anya and the gentlemen only have one case, so their portraits are handled as a composited sprite + background. As such, I wasn't sure which category to put them under. I've put them under "portrait" for now for, but because they're full-screen portraits they cover the entire background image. I'm happy to move them to "background" if you think that would make more sense.

I've checked all the test cases and they should all be correct. All of the test cases are actual screenshots from the game and all match the original game exactly. Only thing to be aware of here is that the original game has a bug that makes the colours wrong when you first enter a dialogue scene -- the colours fade in from black, but there's an off-by-one error that causes them to be slightly darker than they should be until the scene changes and the palette is reloaded. As such, all test cases are taken from after that first scene change to ensure all the colours are correct.