Closes #272

Closes #367

Closes #218

Merge branch 'fix-no-files-found-on-reload' of https://github.com/Ferada/feh into Ferada-fix-no-files-found-on-reload

Merge branch 'custom-background-color' of https://github.com/ulteq/feh into ulteq-custom-background-color

Closes: #382, #384

This introduces a new feh_should_ignore_image function which is called
at appropriate places in those modes to skip images which are loadable but
undesired.

Merge branch 'dimension-pruning-without-preload' of https://github.com/ulteq/feh into ulteq-dimension-pruning-without-preload

Closes #381

FWIW: This behaviour was already present before
394517d1

* Prevents nasty loading loops

* Prevents zombie subprocesses

* Fixes the conversion timeout detection routine

Halves the start-up time of the slideshow if the title contains data from 'file->info'