GitLab

Add openjpeg dependencies to openjpeg build recipe.

Remove openjpeg as dependency for tiff (doesn't appear to be found during tiff
build).

Refactor cmake into own routine.

Disable bzip2 build for OSX.

library_builders.sh script in fact needs common_utils.sh.  Source that
script, and put a guard in common_utils.sh to prevent it being sourced
more than once.

Make function to download and unpack archives.

This allows caching the archives in the `archives` directory, either by
committing to the git repo, or when doing repeated builds of the same
library.

Also, enable encoding on basis of
https://gitlab.dkrz.de/k202009/libaec/blob/master/doc/license.txt

Make configuration more general.

Move responsibility for source futzing back to the travis.yml file,
because we are now doing only one build per job.