Fix for year zero bug and update to d3 libraries

This is the fix for issue #20. It's coming from my personal fork since it was done on my own time rather than work time.

I've also updated the d3 library files, which is probably a good idea to do anyway. d3.geo.projection.v0.min.js now seems more sensitive to the file encoding the server sets, so make sure to serve it as UTF-8.