Now we can use --layer multiple times to modify the --save-as and
--sheet behavior to render only the filtered/selected layers. This can
be combined with --split-layers too.
This change was done to avoid calling split_string() each time we want
to know the frame range. (As the frame range will be used in several
parts of the code.)
We’ve moved the cli into its own directory (src/app/cli). Also, we’ve
added a new “--preview” parameter to know what will be done using the
given command line options.
