Map zoom + coffeescript compilation

Edited gulpfile to live-compile coffeescript in `./public/b-*/b-*.coffee`; this enables editing and changes within those files without separate compilation step.

Added zoom in/out functionality to map.  Looks like we will need to create separate `path` elements for each country to get finer-grained behavior.  But the current approach has a nice effect anyhow.

Minor improvement to map resize on window resize.  Never seen d3 before today, so will need to look into docs a bit closer to polish it more.
One of the annoyances of CoffeeScript is that it always returns last object referenced (or it's trying to protect us from ourselves, not sure -_-): https://github.com/jashkenas/coffeescript/issues/899#issuecomment-590062

So you're actually returning the result of `countryContainer.transition()` here. In this case it works but sometimes it causes unexpected errors. This is why I write `return` at the end of all functions w/o a return value to be more implicit.