Chore: Migrate github.com/chai2010/webp to github.com/davidbyttow/govips

[mkalus]

Pull Request Template

Description

As discussed in #44, I have switched from github.com/chai2010/webp to the "officially" supported library github.com/davidbyttow/govips (supported by libvips that is).

Fixes #44

Type of change

• Changed images conversion to use libvips, if supported.
• The only unsupported format is BMP - I have changed the code to use golang.org/x/image in this case.
• Updated golang.org/x/image to v0.15.0
• Cleaned up some code parts.

How Has This Been Tested?

Ran the tests images_test and documents_test - works.

Also created Docker image using linux amd64 - since you use debian based Docker images, I do not see any problem creating creating images for other platforms (libvips is in all of those).

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have checked my code and corrected any misspellings

[danvergara]

Hey @mkalus!

I just merged an PR that caused some conflicts with yours. Please resolve the conflicts and I'll review the PR as soon as I can.

[mkalus]

Sorry, I have been quite busy lately, I will create a new PR once I find time.

[danvergara]

Well, no need to, just fix the conflicts. Want me to do that if you're busy? No problem at all. I just didn't want to step on your toes.

[danvergara]

Hey @mkalus!

Do you mind if I fix the conflicts and push the changes to merge this?
This might help us to address #36

[mkalus]

Yes sure - I am drowning in work.