Add code components 366-385; ScrollArea Follow, editor sync

A terminal with history, a Go-colored code block, a log viewer that
follows, a hex viewer, a memory map, a JSON tree, a line diff, a GAME
OVER crash screen, an FPS meter, profiler bars, breakpoints,
variables, command history, a shortcut list, a debug grid, a pixel
editor that exports string art, a palette editor, a sprite sheet, a
glyph map and a 6502 register view.

layout.ScrollArea takes Follow, and ChatLog now uses it. data.TreeNode
takes a Value drawn in its Slot. pixel gains Has, and Sprite.Art
writes MustSprite art. pixel.Editor takes the caller's value at each
input event, so a value changed between frames is never typed onto.

code/variables.go

@@ -0,0 +1,54 @@
+package code
+
+import (
+	"strings"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/data"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+// Var is a name, type and value; structs have fields.
+type Var struct {
+	Name, Type, Value string
+	Fields            []Var
+}
+
+type VariablesOptions struct {
+	// Width is in dots; zero means 200.
+	Width    int
+	Disabled bool
+}
+
+type VariablesResult = data.TreeResult
+
+// Variables lists names, types and values; fields open below.
+func Variables(c *ui.Context, text string, vars []Var, selected *string, o VariablesOptions) VariablesResult {
+	return data.Tree(c, text, nodes(vars), selected, data.TreeOptions{Width: pixel.Or("Variables Width", o.Width, 200), Disabled: o.Disabled})
+}
+
+// nodes are vars as tree nodes, values colored by kind.
+func nodes(vars []Var) []data.TreeNode {
+	var out []data.TreeNode
+	for _, v := range vars {
+		out = append(out, data.TreeNode{Label: v.Name + ": " + v.Type, Value: v.Value, Slot: kind(v), Children: nodes(v.Fields)})
+	}
+	return out
+}
+
+// kind is a value's slot, read from its type.
+func kind(v Var) pixel.Slot {
+	t := v.Type
+	switch {
+	case v.Value == "nil":
+		return pixel.Faint
+	case t == "string":
+		return pixel.Good
+	case t == "bool":
+		return pixel.Info
+	case t == "byte" || t == "rune" || strings.HasPrefix(t, "int") || strings.HasPrefix(t, "uint") || strings.HasPrefix(t, "float") || strings.HasPrefix(t, "complex"):
+		return pixel.Warn
+	}
+	return pixel.Faint
+}