Move error types to its own file

errors.go

@@ -0,0 +1,33 @@
+package task
+
+import (
+	"fmt"
+)
+
+// ErrNoTaskFile is returned when the program can not find a proper TaskFile
+var ErrNoTaskFile = fmt.Errorf(`No task file found (is it named "%s"?)`, TaskFilePath)
+
+type taskNotFoundError struct {
+	taskName string
+}
+
+func (err *taskNotFoundError) Error() string {
+	return fmt.Sprintf(`Task "%s" not found`, err.taskName)
+}
+
+type taskRunError struct {
+	taskName string
+	err      error
+}
+
+func (err *taskRunError) Error() string {
+	return fmt.Sprintf(`Failed to run task "%s": %v`, err.taskName, err.err)
+}
+
+type cyclicDepError struct {
+	taskName string
+}
+
+func (err *cyclicDepError) Error() string {
+	return fmt.Sprintf(`Cyclic dependency of task "%s" detected`, err.taskName)
+}