Upgrade Yogi example and migrate to elm-package

This upgrades the Yogi example to `elm-html 1.0.0` and migrates to
elm-package. I also updated the README for `elm-reactor` instructions
instead of using `elm-make`.
Upgrade TextReverser to elm-html 1.0
Merge pull request #21 from passy/example-update

Update examples for elm-html 1.0