Command line argument naming should follow UNIX conventions

[mjuric]

Unix programs these days typically follow the GNU conventions for command line arguments. We deviate from them in two ways:

• Have short arguments with more than one character (e.g. -cp in sorcha run). This is ambiguous with shortening -c -p as -cp (see the second bullet here), and makes argparse disable this feature entirely.
• Have long arguments with underscores (_). This goes against GNU conventions (quote: "Long options consist of -- followed by a name made of alphanumeric characters and dashes."), but more importantly it makes our code feel a bit unnatural (very Java-ish). E.g., run git add --help or ls --help (on linux) to see the difference.

I propose we fix this now, before the cmdline API is frozen for v1.0 -- it will be very hard (impossible) to change later. The fix is easy (I'm volunteering to do it).

[mjuric]

Current WIP prototype (early comments welcome):