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/glob.go

@@ -0,0 +1,32 @@
+package ast
+
+import (
+	"fmt"
+
+	"gopkg.in/yaml.v3"
+)
+
+type Glob struct {
+	Glob   string
+	Negate bool
+}
+
+func (g *Glob) UnmarshalYAML(node *yaml.Node) error {
+	switch node.Kind {
+	case yaml.ScalarNode:
+		g.Glob = node.Value
+		return nil
+	case yaml.MappingNode:
+		var glob struct {
+			Exclude string
+		}
+		if err := node.Decode(&glob); err != nil {
+			return err
+		}
+		g.Glob = glob.Exclude
+		g.Negate = true
+		return nil
+	default:
+		return fmt.Errorf("yaml: line %d: cannot unmarshal %s into task", node.Line, node.ShortTag())
+	}
+}