[RFC] Urgrep: New ELPA submission (eventually)

[Jim Porter]

(Resending; sorry if you get duplicates.)

A while back, I made a package called Urgrep ("Universal Recursive Grep" 
- <https://github.com/jimporter/urgrep>), and now that it's pretty 
stable, I'm starting preparations to submit it to GNU ELPA. I'm not 
*quite* ready to submit it for real, but I'm reasonably close and wanted 
to get some wider feedback before I actually do submit it. If you have 
any suggestions, questions, etc, I'm happy to hear them.

A brief summary: Urgrep is designed to provide a universal interface on 
top of all "recursive grep"-like commands, from ripgrep to git grep to 
the classic find+grep. I made it to solve a frustration I had with other 
similar packages: they're primarily built to support a *particular* 
searching tool, and while some can be coaxed into running with other 
tools, it doesn't always work. Even when it does, it's usually not 
seamless, especially when you add Tramp to the equation.

With Urgrep, you can use *any* rgrep-like command[1]. It will 
automatically use the best tool on the system in question, so if some 
remote host doesn't have your favorite tool, it'll still work just fine.

I also added some Isearch-like bindings in the main function's prompt 
(creatively named 'urgrep'). These all start with M-s and let you set 
common search flags, like number of context lines. Maybe there's a 
better way to do this; the current method seemed reasonable to me, but 
I'm certainly open to suggestions. (I looked at transient.el, but it 
didn't seem like the best fit in this case; maybe I just don't know 
enough about transient.el though.)

Again, I'm not quite ready to submit this to GNU ELPA, but I think it's 
stabilized enough that it's worth getting some more eyes on it in case I 
missed something.

- Jim

[1] If it doesn't support your favorite one out of the box, you can add 
your own support: you just need to add to 'urgrep-tools' with the right 
mappings for the various flags.