Add deadgrep-file-type-alist to allow user-defined easily toggle-able set of types

[gvol]

As usual when writing elisp, I mostly stopped once I got it working, so feel free to make me fix a few things that don't match your code style or quality.

In particular, I wasn't sure if all should be part of the introduced alist or not—I could go either way. I left it as being special, but I'm happy to change it. I'm also not sure what order the buttons should be in. I kind of think they type and glob should be last since they are the most ad-hoc, but I imagine that I will set deadgrep-file-type-alist by project, so it might also be nice to have the "global" one be in more stable positions.

Also, I'm happy to add more tests if you think they are warranted. I couldn't find any other tests about creating or interacting buttons for example.

I do have papers signed with the FSF in case that's a concern.

[gvol]

Sorry, I hate to bug you, @Wilfred, but do you know what I should do to get the tests passing? I've never actually used Travis before and Cask only a little.

[Wilfred]

I've moved the tests from Travis to GitHub actions, and they should now be passing :)

[gvol]

Okay, I rebased on master. Hopefully, they'll pass now.

[gvol]

Sorry it took me so long to get back to this. I rebased on master again and updated my tests for changes on master.

[gvol]

Thoughts, @Wilfred?

[gvol]

I've been using this for a while now, and I find it extremely useful. Is there anything you would like me to do?

[arafel]

Hi - just wondering if there was any chance of this being merged? deadgrep's really useful, but the company I work for uses '.inc' for a lot of their Makefiles - it would be really useful to be able to add a type which searched those as well as normal Makefile names. :-)

[gvol]

Here's what the results might look like, just as an example:

[gvol]

Since you recently merged #138, maybe I'll gently poke you about this one as well. ❤️