Add a Changes doc

CHANGES.md

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+
+## Planned for v0.3.0
+
+  - automatically wrap subscriptions in a `reaction`  (removing the need for over
+    10 keystrokes per handler!!).  Just kidding there are better reasons than that.
+  - produce a more fully featured todomvc (beyond the standard one), todomvc-with-extras
+    - use `enrich` to handle todo duplication
+    - show testing
+    - show debug
+  - begin to use goog.Logger ??  How to let client apps know about exceptions, etc ??
+
+
+## v0.2.0  (2015-03-06)
+
+Being blocked by:
+
+In todomvc, to be done tomorrow ahead of release:
+  - fix bug in todomvc  which means the footer disappears and doesn't come back.
+  - add localstorage
+  - add history, back button etc.
+
+### Breaking
+
+Renames:
+  - `register-pure-handler` renamed to `register-handler`  (and existing low level `register-handler` becomes `register-handler-base` but is not a part of the API).
+  - remove `apply-event` middleware and replace with similar `trim-v`
+  - rename `register-subs` to `register-sub`  (avoid confusion over possible plurals)
+  - rename `set-max-undos`  to `set-max-undos!`
+
+Changes:
+  - `undoable` middleware is now a factory. Where before you used this `undoable`,
+     you must now use this `(undoable "some explanation")`.  See further below.
+
+### Headline
+
+  - example `todomvc` available in examples folder.
+  - Wiki documentation is now more substantial.
+  - introduce some new handler middleware: `debug`, `enrich` and `after`
+
+### Other:
+  - exceptions in a go loop are a special type of hell.  Improve the reporting of exceptions happening in event handlers.
+  - allow Middleware to be registered as a vector.  data > functions > macros
+  - fix two bugs in undo implementation
+  - name licence file correctly, thanks to @smith
+  - fix typo in readme, thanks to @btheado
+  - Readme now admits to 200 lines of code, not 100.
+  - dispatch now explicitly returns nil
+  - travis integration (not that we have any tests currently)
+
+
+
+### Details On Undo Changes
+
+We've made changes so that the undo/redo feature is more powerful.  Associated
+with each undo state is an explanation which can be presented to the user to
+inform them as to the actions they will be undoing or redoing.
+
+Previously `undoable` was simply middleware, but it is now a middleware factory.
+
+Essentially that means you can't use it "plain" anymore, you must call it to
+get middleware (put it in `()`) and, when you do, supply a parameter which is
+an explanation for the mutation. "Set spam flag to yes",  "add todo", etc.
+
+When the time comes to present undos to the user, you then have an explanation
+associated with each one.
+
+The `explanation` provided to undoable must be either a `string` (static
+explanation) or a function  `(db event) -> string`  (allowing you to customize
+the undo message based on details of the event.  "Added todo called blah blah blah").