Switch playground to use e.g. Monaco editor

[polytypic]

Currently the playground uses Klipse which uses CodeMirror. It works fine, but an editor like Monaco could fairly easily be configured to provide completion and online documentation.

[smeijer]

When working on a new playground, I think it would be awesome to add a small performance test loop to it. It doesn't need to be as advanced as jsperf, but a simple test so we can see how good a implementation of specific lenses perform.

The parsing of code in the playground can take some time, when a data object becomes larger (L.collectAs(myFn, [L.elems, 'sub', L.elems, 'path', L.choose....], largeDataObject). Being able to run the final L statement in a loop, would give some helpful feedback.

[polytypic]

Hmm... Interesting idea! Note that all the current interactive pages (playground, exercises, and readme) use the development (rather than production) browser build of the library, which includes extra run-time checking code and runs significantly slower than the production build. So, it might be useful to have a separate benchmarking page with the production build.