Support for GY-88 added

This Chinese IMU board becomes very popular and contains already supported chips.
Amazon: http://www.amazon.com/Happy-Store-MPU-6050-HMC5883L-Control/dp/B00G8T6ZVK
AliExpress: http://www.aliexpress.com/item/GY-88-10DOF-IMU-MPU6050-HMC5883L-BMP085-for-Arduino-Accel-Gyro-Baro-Mag-UNO-Mega-DUE/1377907454.html