It's awkward to work on fn.dart in the examples directory so this CL moves it
to /sky/framework. Also, I've merged the whole library into one file instead of
using the |part| mechanism. The whole thing isn't that big.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/987463002

This is just a proof of concept. If we like this direction, it will move out of the examples directory (likely re-written) and be committed in smaller pieces with unit tests and formal reviews.

TBR=abarth
BUG=

Review URL: https://codereview.chromium.org/971183002