Some crashes fixed and interface changed.
IMU is not calibrated if no -imu param is given (prevents crash).
Crash fixed at the end of a sequence when -cam log://.
Option changed: exit on finish true by default.
Option changed: poly3 distortion model used by default.
Option added: key '[' starts calibration.
Merge pull request #5 from arpg/fix/crashes

Some crashes fixed and interface changed.