add knockback3 package

[Cokemonkey11]

See https://github.com/peq/WurstScript/pull/472 for history and discussion

[Frotty]

[00:22] @Frotty: the system should not hardcoded destroy destructables, add some short description at the top if you want this to be done with 0 ENUM_SIZE, or offer a listener, code var, whatever

Also you could add configuration to only destroy trees and not all destructables. But then again, offering a way to add a listener would let the user do this instead.

[Cokemonkey11]

@Frotty regarding tree checking, Knockback3D for vJass supports it, but it uses IsDestructableTree library which we don't have so I removed it.

http://www.wc3c.net/showthread.php?t=103927

[Cokemonkey11]

@Frotty agree that adding proper listener would be ideal but I think there's a lot of code shared with colliders. I think this should be a separate topic.

This should be ready now.

[Frotty]

I think what many people want from a 3d knockback is also a jump like function, ie being able to specify a target position and the knockback will be set so that the unit lands on the target pos. please provide an overloaded add function with different parameters. Otherwise looks gut so far 🍰

[Cokemonkey11]

@Frotty done :) and there's a cute demo in the demo map too

[Frotty]

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