golangci-lint configuration file

golangci-lint can run all the currently enabled linters, and as far as I
can tell, does it in under 5 seconds as opposed to over 180 seconds
(compare `time make cilint` and `time make lint`).

Some of the linters that are listed in the "enabled" section but
commented out looked like a good idea to me, and fairly low hanging
fruit to fix, but they are not passing at the moment.

All the linters covered in the current Makefile are run.

TODO:
- replace lint target in Makefile with golangci-lint
- remove .github/workflow/errcheck.yml

modules/transmission/display.go

@@ -57,11 +57,12 @@ func (widget *Widget) torrentPercentDone(torrent *transmissionrpc.Torrent) strin
 	pctDone := *torrent.PercentDone
 	str := fmt.Sprintf("%3d%%↓", int(pctDone*100))
 
-	if pctDone == 0.0 {
+	switch pctDone {
+	case 0.0:
 		str = "[gray::b]" + str
-	} else if pctDone == 1.0 {
+	case 1.0:
 		str = "[green::b]" + str
-	} else {
+	default:
 		str = "[lightblue::b]" + str
 	}