AP_HAL_FLYMAPLE: Sensor reading improvements

I2C speed increased to 400kHz
Accelerometer 8g max, Normal power, 800Hz bandwidth
Gyros: 2000 degrees/sec, 256Hz LPF, 8kHz internal sample rate
AP_HAL_FLYMAPLE: UARTDriver libmaple internal ring buffers enlarge on demand
AP_InertialSensor: Formalise and document Flymaple Gyro scaling factor
AP_InertialSensor: Added examples/Flymaple for testing
AP_InertialSensor: Flymaple now polls sensors at 800Hz. More changes to
come...
AP_InertialSensor: Flymaple sensors improvements

Flymaple sensors are now raw sampled at 800Hz, and LowPassFilter2p is used
to filter to the desired filter cutoff frequency.
Flymaple sensor polling is done in the main thread NOT in the timer
interrupts.
AP_InertialSensor: mark flymaple as nobuild

won't build with build_examples.sh script