all: rename the gioui.org/ui module to gioui.org

The "ui" is redundant and stutters.

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

layout/doc.go

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+/*
+Package layout implements layouts common to GUI programs.
+
+Constraints and dimensions
+
+Constraints and dimensions form the interface between layouts and
+interface child elements. This package operates on Widgets, functions
+that compute Dimensions from a a set of constraints for acceptable
+widths and heights. Both the constraints and dimensions are maintained
+in an implicit Context to keep the Widget declaration short.
+
+For example, to add space above a widget:
+
+	gtx := &layout.Context{...}
+	gtx.Reset(...)
+
+	// Configure a top inset.
+	inset := layout.Inset{Top: ui.Dp(8), ...}
+	// Use the inset to lay out a widget.
+	inset.Layout(gtx, func() {
+		// Lay out widget and determine its size given the constraints.
+		...
+		dims := layout.Dimensions{...}
+		gtx.Dimensions = dims
+	})
+
+Note that the example does not generate any garbage even though the
+Inset is transient. Layouts that don't accept user input are designed
+to not escape to the heap during their use.
+
+Layout operations are recursive: a child in a layout operation can
+itself be another layout. That way, complex user interfaces can
+be created from a few generic layouts.
+
+This example both aligns and insets a child:
+
+	inset := layout.Inset{...}
+	inset.Layout(gtx, func() {
+		align := layout.Align(...)
+		align.Layout(gtx, func() {
+			widget.Layout(gtx, ...)
+		})
+	})
+
+More complex layouts such as Stack and Flex lay out multiple children,
+and stateful layouts such as List accept user input.
+
+*/
+package layout