AutoOrient to automatically fix orientation of images based on EXIF orientation flag

[LeoAdamek]

This PR adds a new func to the bimg.Image type AutoOrient which will perform the required processes to correct the orientation of the image based on the EXIF orientation flag.

[h2non]

Please, take a look to my comments.

[h2non]

You might consider using bimg.Angle here. See:
https://github.com/h2non/bimg/blob/master/options.go#L57-L74

[h2non]

Note that this capability aims to be implemented here:
https://github.com/h2non/bimg/blob/master/resize.go#L501-L537

I think this would be redundant. Perhaps makes more sense to merge code into the existent code.

[LeoAdamek]

@h2non Thanks for the feedback, didn't see this func because its not exported.

Agreed there may be some redundancy here, but would it not make sense for this feature to behave in the same way the other "convenience" methods?

Is your suggestion that there be an AutoOrient bool property on the Options struct which will run the calculateRotationAndFlip function from resize.go ?

-Leo

[h2non]

Is your suggestion that there be an AutoOrient bool property on the Options struct which will run the calculateRotationAndFlip function from resize.go ?

The intended default behavior is to process images with auto orientation, unless you explicitly want to disable that behavior via:
https://github.com/h2non/bimg/blob/master/options.go#L201

I agree about exposing that capability as part of the public API.
Perhaps we should simply converge both functions into a single one which is also exported.

[LeoAdamek]

In which case, would an AutoOrient function just pass an empty Options{} struct to resize and return that?

My my use case, I need to have the image correctly oriented for later processing, including being able to get the dimensions with that orientation applied.

[h2non]

This should be already fixed by #183. Feature is now available in bimg v1.0.11+.