Add '-p' as a shortcut for '--style=plain'

[sharkdp]

The "plain" style is sometimes desirable to copy&paste from the terminal without the line numbers or Git modifications. There should be a short option (-p) that can be used to set --style=plain.

[ms2300]

Can I help out and add this feature in?

[sharkdp]

Yes, absolutely! Any help would be greatly appreciated.

[sharkdp]

Closed via #222