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/gcal/display.go

@@ -147,11 +147,12 @@ func (widget *Widget) timeUntil(calEvent *CalEvent) string {
 	untilStr := ""
 
 	color := "[lightblue]"
-	if days > 0 {
+	switch {
+	case days > 0:
 		untilStr = fmt.Sprintf("%dd", days)
-	} else if hours > 0 {
+	case hours > 0:
 		untilStr = fmt.Sprintf("%dh", hours)
-	} else {
+	default:
 		untilStr = fmt.Sprintf("%dm", mins)
 		if mins < 30 {
 			color = "[red]"