Rename lib to src

This is a first step towards making Monarch compatible with
client-side setups other than sprockets-style script
concatenation (browserify, inclusion of a single script).
We'll need to provide already-compiled and concatenated
javascript files for `client` and `client_test_support`. I'd
like to put these scripts in the `lib` directory, and put
the original coffeescript files in `src`, the way other
coffeescript modules do.
Make Monarch browserify-compatible

- If a CommonJs module system is detected, client-side code
will require its dependencies and set `module.exports.
Otherwise, it will set `window.Monarch` as usual.
- The `package.json` now includes entry points for node
and browserify.
- All entry point files now live in `lib`. This includes
the server-side entry point, the concatenated javascript
files generated by running `cake build`, as well as
sprockets-compatible manifest files, which have the suffix
`.dev`.