* add transform-class-properties to stage 3, set spec mode to default
* update readme with examples; use `buildUndefinedNode()`; change behavior to always define both static and nonstatic class properties regardless of spec/loose mode; update tests
The PathHoister ignored member references on "this", causing it
to potentially hoist an expression above its function scope.
This patch tells the hoister to watch for "this", and if seen,
mark the nearest non-arrow function scope as the upper limit
for hoistng.
This fixes#4397 and is an alternative to #4787.
