Improvements to the online version

[thibautbenjamin]

In #58, the online version is completely overhauled, and now has a mini code-editor. This is a bare bone version, and it would be improved in many ways:

• Handle error reporting better to print terminal codes for coloring, and color things that are printed on stdout
• add syntax highlighting for catt
• add a button to load examples from the repos directly in the context
• add buttons to save/load files (this is annoying as it might require a local server)
• add a toggle to drop into interactive mode

Relevalnt link for setting up the syntax highlighting: https://css-tricks.com/creating-an-editable-textarea-that-supports-syntax-highlighted-code/