refactor: we don't wanna export pkg/oonimkall/tasks (#216)

* doc: merge the engine and the cli readmes

Part of https://github.com/ooni/probe/issues/1335

* refactor: we don't wanna export pkg/oonimkall/tasks

See https://github.com/ooni/probe/issues/1335

pkg/oonimkall/internal/tasks/eventemitter.go

@@ -0,0 +1,40 @@
+package tasks
+
+// EventEmitter emits event on a channel
+type EventEmitter struct {
+	disabled map[string]bool
+	out      chan<- *Event
+}
+
+// NewEventEmitter creates a new Emitter
+func NewEventEmitter(disabledEvents []string, out chan<- *Event) *EventEmitter {
+	ee := &EventEmitter{out: out}
+	ee.disabled = make(map[string]bool)
+	for _, eventname := range disabledEvents {
+		ee.disabled[eventname] = true
+	}
+	return ee
+}
+
+// EmitFailureStartup emits the failureStartup event
+func (ee *EventEmitter) EmitFailureStartup(failure string) {
+	ee.EmitFailureGeneric(failureStartup, failure)
+}
+
+// EmitFailureGeneric emits a failure event
+func (ee *EventEmitter) EmitFailureGeneric(name, failure string) {
+	ee.Emit(name, EventFailure{Failure: failure})
+}
+
+// EmitStatusProgress emits the status.Progress event
+func (ee *EventEmitter) EmitStatusProgress(percentage float64, message string) {
+	ee.Emit(statusProgress, EventStatusProgress{Message: message, Percentage: percentage})
+}
+
+// Emit emits the specified event
+func (ee *EventEmitter) Emit(key string, value interface{}) {
+	if ee.disabled[key] == true {
+		return
+	}
+	ee.out <- &Event{Key: key, Value: value}
+}