Providing several config files

[jbriales]

I read through the docs but didn't found anything about this:
Would it be possible in CLI11 to take several input config files, and just concatenate their entries?
Currently if I provide --config more than once I just get:

--config: At Most 1 required but received 2

The motivation would be to be able to reuse multiple subsets of options and combine them.

[phlptp]

I don't think it is currently handled but I don't think the modification would be that hard.