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.
Not necessary but just FYI - CoffeeScript likes you to use its features when possible. In this case, it's not necessary to have `()` here since there are no args. See: https://github.com/polarmobile/coffeescript-style-guide#functions