Add support for smart TXAN

[Iritscen]

Leaving this here as more of an idea than a request. TXANs are extremely inefficient with memory and disk space because they don't support variable timing. If, like a GIF, each frame could have its own timing, then concepts would be possible such as animated faces that blink. A randomization factor could also be supported. A resting state (the frame with eyes closed) could also be defined for use when characters die.

Other applications such as blinking electronics on a high-tech combat uniform would be possible. This feature could also be extended to support lip flap, i.e. animated faces in cutscenes.

There is only one extant TXAN in Oni (TXMPNEWSGUY02) so it's easy to extend the format without breaking existing content.