TX_START/TX_END support

[DeathEgg]

Doom Wiki entry

Basically skips the arduous process of adding a texture to the WAD, adding to PNAMES and then adding to TEXTURE1/TEXTURE2 by just placing it between TX_START/TX_END. Downside of this method is you can't put patches on top of each other this way but that's what TEXTURE1/TEXTURE2 is for. (Also you could probably skip on the PNG support it mentions)