[feature] Add args_override_self(true)

[bryceberger]

Reasoning: I would like to make an alias to change some default behavior (sort, prefixes (future), etc). However, supplying the same argument twice (et -s name -s size) is an error.

Current behavior: et -s name -s size will not execute, with the message (from clap) that --sort cannot be used multiple times.
Expected behavior: et -s name -s size will execute, and sort output by size.

(This is a 3 line change and I have a PR ready, just wanted approval first as stated in the readme)

[solidiquis]

Feel free to submit the PR!

[solidiquis]

#35