I've also removed the top-level description of the Sky package. Instead, we
should host that content on flutter.io.

If the build stack got long before, it would get cropped.

These files really belong on other libraries.

revert PATH changes

fix typo

some dartdoc changes in files

Code outside of package:sky should import this code using

package:sky/rendering.dart
package:sky/widgets.dart

Moving this code into the "src" directory is a convention that signifies that
and it cleans up the generated dartdoc because the libraries in the src
directory aren't included in the generated documentation. Instead, the classes
are documented in the widgets.dart and rendering.dart libraries.

... and other code in object.dart.

I'll write the Widget wrapper in the next CL, including adding
support for padding at the Widget layer.

@Hixie

Similar to widgets.dart, rendering.dart exports the entire rendering layer.
Also, update the examples to use rendering.dart and widgets.dart. Also clean up
some exports so that the examples have more sensible imports.