The new class Direction will be used to represent the direction of a
calibration request.
Update posexcept.hh to add new exception bad_direction, used in class
Direction.
- Add files posexcept.{hh,cc} that contains exception classes.
- Add class Input, that handles InputMedium (and InputLogMedium, in the
future). Note that for the moment, the unit test is *very* minimal.
- UserInterface: Add options for the input medium and the CSV file.