Switch debugger for pry-debugger
Remove the explicit rack dependency

Rack is just a dependency of Rails. This was here because the app used to need a specific version from Github.
Avoid losing sensor results by buffering reads

Added BufferedSerialDevice to act as a device and buffer partially read lines.
BufferedSerialDevice uses the iobuffer gem rather than monkeypatching IO.
Using BufferedSerialDevice instead of SerialPort directly allows us to give it a path instead of adding it to each object via metaprogramming.

Fixes #27