Add ROOT_DIR and TASKFILE_DIR special variables

Closes #215

taskfile/read/taskfile.go

@@ -144,6 +144,7 @@ func Taskfile(readerNode *ReaderNode) (*taskfile.Taskfile, error) {
 				task.Dir = filepathext.SmartJoin(dir, task.Dir)
 				task.IncludeVars = includedTask.Vars
 				task.IncludedTaskfileVars = includedTaskfile.Vars
+				task.IncludedTaskfile = &includedTask
 			}
 		}
 

taskfile/task.go

@@ -26,6 +26,7 @@ type Task struct {
 	Run                  string
 	IncludeVars          *Vars
 	IncludedTaskfileVars *Vars
+	IncludedTaskfile     *IncludedTaskfile
 }
 
 func (t *Task) Name() string {