Added a live code editor based on Ace.js and rust-playpen. Features include:

1) Sample code can be edited and run in place.
2) Results/errors are color-coded and displayed in place.
3) Lines/text with errors are highlighted in the editor.
Merge pull request #26 from SergioBenitez/gh-pages

Added a live code editor based on Ace.js and rust-playpen.