Codepoints

This adds codepoints support to node-fontnik. A sync function called
`codepoints(str:facename)` returns an array of numbers indicating
Unicode code points covered by the font. Implements #56
Removing this `break;` should enable support for testing the codepoints in an entire fontstack instead of just the first font, right? Was talking with @nickidlugash last night about how this could be useful.