Arrays to buffers

Change our writes to use buffers instead of arrays so node Writable streams don't complain. We haven't seen this issue with `node-serialport` because it [auto converts arrays to buffers](https://github.com/voodootikigod/node-serialport/blob/master/serialport.js#L162) but other output streams do not.

I rebased this branch off of #43 and make the necessary changes so the tests won't break. This was needed because tests use `Array#indexOf` a lot.