Terminate write and control threads in shell thread.

Terminate both write and control threads in SampleAndControl::Stop()
instead of using nested chThdWait() commands.
Fix CMAKE_FIND_ROOT_PATH in CMake toolchain file.
Remove call to chThdSleepUntil() in control loop.

Occasionally, the control loop will take longer than expected (5ms) and
will chThdSleepUntil() missing the deadline and sleeping for a long
period of time instead.  The conditional statement in chThdSleepUntil()
will always evaluate to true since time and chTimeNow() are both
unsigned.
Discussed here: http://sourceforge.net/p/chibios/bugs/332/
Add Message_np Python class.

The Message_np class takes the Python Protobuf output and creates numpy
datatypes to facilitate plotting collected data.
Convert protobuf messages to numpy dtypes.

Add methods to Message_np to convert messages. Add plotting example.
Rename fields in samples.proto.

Rename all fields using lower_case_with_underscores style except for
fields representing mathematical variables.
Add data plotting script.
Fix number of bytes when writing to disk.

Move protobuf message encoding and buffer logic to write thread. All
calls to f_write now write a fixed amount of bytes to disk.
Slow I2C pin speed and set CH_TIME_QUANTUM to 0
Merge remote-tracking branch 'oliverlee/dev' into dev
Switch i2c back to 400kHz fast mode.
Prevent post-checkout from running on a file.
ChibiOS-RT update.