Specifying duplicate options on the CLI overrides previous options silently

[clintval]

In using the expressive CLI, I tried to see if I could unpack the "list-like" options by specifying the command line flag more than once. For example:

splitcode \
    --extract "0:0<umi[9]>" \
    --extract "<cb{@cb1}>"

I was hoping this would emulate:

splitcode \
    --extract "0:0<umi[9]>,<cb{@cb1}>"

Instead, the program overrides the previous value with the most recent value silently instead of raising an exception. If possible, it would be a major boost to splitcode CLI readability if handling list-like options could be supported by specifying the command line flag more than once.

For some inspiration look towards other programs do this well like --include / --exclude options in aws s3 sync.

[Yenaled]

Multiple --extract's are now possible in 0.31.6 -- feel free to open a new issue if there are other similar command-line edits that should be made.