ui/layout: rename and sanitize enums

Rename MainAxisAlignment to Spacing and CrossAxisAlignment to just
Alignment.

Drop the untyped Start, End, Center values and add them as Spacing
and Direction values. Center is both a Direction and Alignment, so
use the synonym "Middle" for the alignment.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/layout/layout.go

@@ -27,6 +27,27 @@ type Dimens struct {
 }
 
 type Axis uint8
+type Alignment uint8
+type Direction uint8
+
+const (
+	Start Alignment = iota
+	End
+	Middle
+	Baseline
+)
+
+const (
+	NW Direction = iota
+	N
+	NE
+	E
+	SE
+	S
+	SW
+	W
+	Center
+)
 
 const (
 	Horizontal Axis = iota
@@ -173,3 +194,54 @@ func (a *Align) End(dims Dimens) Dimens {
 		Baseline: dims.Baseline,
 	}
 }
+
+func (a Alignment) String() string {
+	switch a {
+	case Start:
+		return "Start"
+	case End:
+		return "End"
+	case Middle:
+		return "Middle"
+	case Baseline:
+		return "Baseline"
+	default:
+		panic("unreachable")
+	}
+}
+
+func (a Axis) String() string {
+	switch a {
+	case Horizontal:
+		return "Horizontal"
+	case Vertical:
+		return "Vertical"
+	default:
+		panic("unreachable")
+	}
+}
+
+func (d Direction) String() string {
+	switch d {
+	case NW:
+		return "NW"
+	case N:
+		return "N"
+	case NE:
+		return "NE"
+	case E:
+		return "E"
+	case SE:
+		return "SE"
+	case S:
+		return "S"
+	case SW:
+		return "SW"
+	case W:
+		return "W"
+	case Center:
+		return "Center"
+	default:
+		panic("unreachable")
+	}
+}