Add straightforward version printing to stdio.

[boyanpenkov]

This adds a tiny convenience function, so that

papers status --version

will show you the version of the currently installed papers you have, so that you can figure out if papers in $PATH is what you think it is.

[boyanpenkov]

Confirming all tests pass, but only have tested on linux.

[perrette]

Good point. As a general comment and before seeing the code, I'd argue it would be more useful or usual to have it at the root level papers --version. Additionally, version number could be added to the header during status printing.

[boyanpenkov]

set and set.

[perrette]

Excellent. I'll take another look this evening (CET Berlin/Italy). First impression:

• one liner print(papers.__version__) would work too
• might need an parser.exit(0) to end right after printing with papers --version
• instead of statuscmd(), it would be tidier IMO to write the print inside the Config.status() method. For example, write it right in the header as papers configuration (global) v2.3.1, or possibly as footer after the last line. Possibly simply v2.3.1. I'd need to see it to get a firm impression. What do you say?

[boyanpenkov]

Excellent. I'll take another look this evening (CET Berlin/Italy). First impression:

* one liner `print(papers.__version__)` would work too

Done.

* might need an `parser.exit(0)` to end right after printing with `papers --version`

I guess, if you want to, since it's meant to be human-readable for stdio, I find the help info useful. If someone starts calling this externally and wants only the string, we can do this then?

* instead of `statuscmd()`, it would be tidier IMO to write the print inside the `Config.status()` method. For example, write it right in the header as `papers configuration (global) v2.3.1`, or possibly as footer after the last line. Possibly simply `v2.3.1`. I'd need to see it to get a firm impression. What do you say?

Done, I just hadn't gotten to reading config.py yet. I do think the full version string is a better idea, so then folks don't mess up 2.3.1 vs 2.3.1+yourlocalchanges.