Simplify repetition of command line arguments

[fpgmaas]

Is your feature request related to a problem? Please describe.

Currently, to ignore multiple dependencies in the same category, or to exclude multiple directories, the flag has to be reused, e.g.

deptry . --exclude foo -- exclude bar --exclude foobar

This can be shortened to

deptry . --e foo -- e bar --e foobar

At the cost of clarity.

Describe the solution you would like

Similar to black and flake8, allow the passing of a list of comma separated values:

deptry . --exclude foo,bar,foobar

This is both short and clear.