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/gitlabtodo/widget.go

@@ -90,7 +90,7 @@ func (widget *Widget) getTodos(apiKey string) ([]*gitlab.Todo, error) {
 func (widget *Widget) trimTodoBody(body string) string {
 	r := []rune(body)
 
-	// Cut at first occurance of a newline
+	// Cut at first occurence of a newline
 	for i, a := range r {
 		if a == '\n' {
 			return string(r[:i])