all: rename package ui to unit

Package ui is now only about units except for the Config.Now method.
Remove Now and rename Config to Converter. Add layout.Config to
replace the old ui.Config.

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

app/window.go

@@ -13,7 +13,7 @@ import (
 	"gioui.org/io/event"
 	"gioui.org/io/profile"
 	"gioui.org/op"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 // WindowOption configures a Window.
@@ -22,7 +22,7 @@ type WindowOption struct {
 }
 
 type windowOptions struct {
-	Width, Height ui.Value
+	Width, Height unit.Value
 	Title         string
 }
 
@@ -86,8 +86,8 @@ var ackEvent event.Event
 // BUG: Calling NewWindow more than once is not yet supported.
 func NewWindow(options ...WindowOption) *Window {
 	opts := &windowOptions{
-		Width:  ui.Dp(800),
-		Height: ui.Dp(600),
+		Width:  unit.Dp(800),
+		Height: unit.Dp(600),
 		Title:  "Gio",
 	}
 
@@ -339,7 +339,7 @@ func WithTitle(t string) WindowOption {
 }
 
 // WithWidth returns an option that sets the window width.
-func WithWidth(w ui.Value) WindowOption {
+func WithWidth(w unit.Value) WindowOption {
 	if w.V <= 0 {
 		panic("width must be larger than or equal to 0")
 	}
@@ -351,7 +351,7 @@ func WithWidth(w ui.Value) WindowOption {
 }
 
 // WithHeight returns an option that sets the window height.
-func WithHeight(h ui.Value) WindowOption {
+func WithHeight(h unit.Value) WindowOption {
 	if h.V <= 0 {
 		panic("height must be larger than or equal to 0")
 	}