Add rotation module and functions

[ripytide]

As a part of image-rs/image#2238

[theotherphil]

Thanks! These should go alongside the existing rotation functions in the (clunkily named) geometric_transformation module.

[ripytide]

I've moved them across 👍

[ripytide]

Do you think we should move the flip functions to geometric_transformations as well since they are like reflections, but then the module might get a bit crowded?

[theotherphil]

Let’s leave them for now and bike shed the module structure with whatever functions we’ve got before the next release :-)

[theotherphil]

I don’t feel strongly either way but it’s a bit unfortunate to use angles in degrees in the names of these functions when angles everywhere else in this file (/crate) are in radians. Can’t think of better names off the top of my head though.

[ripytide]

As some prior art, opencv just has a single rotate() function which takes an enum that looks like ROTATE_90_CLOCKWISE

[ripytide]

Maybe we should do the same and use a single function with an enum, but I don't feel particularly strongly either way.

[theotherphil]

I wondered the same thing. I’ll just merge as is for now. Thanks.