Add ROOT_DIR and TASKFILE_DIR special variables

Closes #215

setup.go

@@ -20,6 +20,10 @@ import (
 )
 
 func (e *Executor) Setup() error {
+	if err := e.setCurrentDir(); err != nil {
+		return err
+	}
+
 	if err := e.readTaskfile(); err != nil {
 		return err
 	}
@@ -53,6 +57,23 @@ func (e *Executor) Setup() error {
 	return nil
 }
 
+func (e *Executor) setCurrentDir() error {
+	if e.Dir == "" {
+		wd, err := os.Getwd()
+		if err != nil {
+			return err
+		}
+		e.Dir = wd
+	} else if !filepath.IsAbs(e.Dir) {
+		abs, err := filepath.Abs(e.Dir)
+		if err != nil {
+			return err
+		}
+		e.Dir = abs
+	}
+	return nil
+}
+
 func (e *Executor) readTaskfile() error {
 	var err error
 	e.Taskfile, err = read.Taskfile(&read.ReaderNode{