Adding another debug level (for all bad events), logging usb underflow.

  modified:   src/pip_sense_layer.cpp
Adding an offline mode that prints packets.

  modified:   CMakeLists.txt
  modified:   src/pip_sense_layer.cpp
Trying to deal with libusb1.0's detached device problems.

Libusb1.0 is terrible at dealing with this. Even the latest version
(1.0.16) does not deal with this properly, although it returns an error
of LIBUSB_ERROR_IO rather than LIBUSB_ERROR_OTHER. Perhaps creating new
context values in libusb_init every time an error occurs can fix this
by forcing libusb to reinitialize its library.

  modified:   src/pip_sense_layer.cpp
Adding extra print statement warning people to sudo.

  modified:   src/pip_sense_layer.cpp