Rename editing2/ and theme2/ to editing/ and theme/.

sky/sdk/lib/README.md

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+SKY SDK
+========
+
+Sky and Sky's SDK are designed as layered frameworks, where each layer
+depends on the ones below it but could be replaced wholesale.
+
+The bottom-most layer is the Sky Platform, which is exposed to Dart
+code as various ```dart:``` packages, including ```dart:sky```.
+
+The [base/](base/) directory contains libraries that extend these core
+APIs to provide base classes for tree structures
+([base/node.dart](base/node.dart)), hit testing
+([base/hit_test.dart](base/hit_test.dart)), debugging
+([base/debug.dart](base/debug.dart)), and task scheduling
+([base/scheduler.dart](base/scheduler.dart)).
+
+Above this are the files in the [painting/](painting/) directory,
+which provide APIs related to drawing graphics, and in the
+[animation/](animation/) directory, which provide core primitives for
+animating values.
+
+Layout primitives are provided in the next layer, found in the
+[rendering/](rendering/) directory. They use ```dart:sky``` and the
+APIs exposed in painting/ to provide a retained-mode layout and
+rendering model for applications or documents.
+
+Widgets are provided by the files in the [widgets/](widgets/)
+directory, using a reactive framework. They use data given in the
+[theme/](theme/) directory to select styles consistent with Material
+Design.
+
+Text input widgets are layered on this mechanism and can be found in
+the [editing/](editing/) directory.
+
+Alongside the above is the [mojo/](mojo/) directory, which contains
+anything that uses the Mojo IPC mechanism, typically as part of
+wrapping host operating system features. Some of those Host APIs are
+implemented in the host system's preferred language.
+
+Here is a diagram summarising all this:
+
+```
+  +-----------------------------+ ------
+  |           YOUR APP          |
+  |     +--------------------+--+ 
+  |     |      [editing/](editing/)      |  |
+  |  +--+-------------------++  |
+  |  |  [widgets/](widgets/)  ([theme/](theme/))  |   |
+  | ++---------------------++   |  Dart
+  | |      [rendering/](rendering/)      |    |
+  +-+---------+------------+    |
+  | [painting/](painting/) | [animation/](animation/) |    |
+  +---------------+--------+    |
+  |    [base/](base/)      |  [mojo/](mojo/)      |
+  +------------+--+-+----+------+ -------
+  |  dart:sky  |    |    | Host |
+  +--------+---+    |    | APIs |  C++
+  |  Skia  |  [Dart](https://api.dartlang.org/)  |    +------+  ObjC
+  +--------+--------+           |  Java
+  |            Mojo             |
+  +-----------------------------+ -------
+  |    Host Operating System    |  C/C++
+  +-----------------------------+ -------
+```
+
+TODO(ianh): document dart:sky and the Host APIs somewhere