refactor: taskfile/ast package (#1450)

* refactor: ast package

* feat: read -> taskfile

* refactor: taskfile.Taskfile -> taskfile.Read

* refactor: move merge function back into taskfile package

* refactor: rename taskfile.go to read.go

taskfile/ast/location.go

@@ -0,0 +1,18 @@
+package ast
+
+type Location struct {
+	Line     int
+	Column   int
+	Taskfile string
+}
+
+func (l *Location) DeepCopy() *Location {
+	if l == nil {
+		return nil
+	}
+	return &Location{
+		Line:     l.Line,
+		Column:   l.Column,
+		Taskfile: l.Taskfile,
+	}
+}