add file ext support

[Capt0rr]

For files that for whatever reason don't have filetype support you can still refer to them as:

settings = {
	['.funkytype'] = {
		"set expandtab on",
	}
}

[mcepl]

Nothing against this PR, but if at least sensible, please file new filetype like for example https://github.com/martanne/vis/pull/933/files.

[Capt0rr]

Thanks for reviewing. I'm no longer using vis so I'm happy with any changes to it or you can close this PR if no one is interested in it.

[mcepl]

I am not the owner (@jocap is), but I have already merged this PR into my repo at https://git.sr.ht/~mcepl/vis-filetype-settings.