Package daybed.js for npm.js

Uses npm.js to package daybed.

It still misses a gulp rule of some sort to generate the daybed.min.js file that should be used by lib authors.
Immediate functions are a general pattern for libs, it keeps the scope safe. And it applies "use strict" to this lib only. Maybe gulp can enclose the lib when we build.

Otherwise, you can keep the function() and remove the whole indentation though.