Document BIK video texture format

[rdw-software]

          Maybe have `BMP, TGA, JPG` as a new category for `Textures`? and more recent version also use `Bink` for textures

"data/model/ad/ad01.rsm" Version(1, 5, 0)
Has texture "ad/01.bik" that is not BMP or TGA.

"data/model/gevent/vrag02_40.rsm2" Version(2, 3, 0)
Mesh "vrag02_40" has texture "gevent/vrag02_40.bik" that is not BMP or TGA.

"data/model/gevent/vrag02_70.rsm2" Version(2, 3, 0)
Mesh "vrag02_70" has texture "gevent/vrag02_70.bik" that is not BMP or TGA.

Originally posted by @hukasu in #94 (comment)

[rdw-software]

Some notes related to this format in case anyone is bored enough to research it:

• BIK is a container format; inside there is video and audio data (not sure if both are supported by the RO client)
• GR2 files also contain Bink-compressed textures; it's unclear whether the format is the same (probably not?)
• Parsing the container is fairly trivial, even if done manually - but the frames and audio tracks are of course compressed
• The audio format may or may not be the same - or derived from - the old Smacker audio codec (needs more research)
• The easiest way to support this format is to just use FFMPEG and convert to, say, h264 - as Korangar does
• To natively support the format, one would need to deal with both compression schemes and avoid licensing issues
• Various details of the format have been described in online resources (e.g., blog by a FFMPEG contributor, RAD devs)

Video textures are extremely niche in the context of the RO client. This is arguably even less useful than GR2 support.