This interface is abstract class.
Includes such methods as initialize, probe, read_temp,
read_acc, read_gyro, read_mag, getMotion6, getMotion9.
Also it has 3 massives for X,Y,Z of acc, gyro, mag and variable
for value of temperature.

Now example AccelGyroMag able to use 2 inertial sensors: MPU9250 and
LSM9DS1. Implemented via abstract class inertial_sesor.
List of changes:
Added parsing of input parameters for choice of sensor.
Created function for allocation selected sensor.
Added information messages.
Rewrited comments to the file about using example.
Added to Makefile target for compilation "Navio/LSM9DS1.cpp".

New driver allows initialize inertial sensor LSM9DS1 and read data
from it. Able findings:
Acclerometer(acc) X,Y,Z (+/- 2/4/8/16 g)
Gyroscope(gyro)   X,Y,Z (+/- 245/500/2000 dps)
Magnetometer(mag) X,Y,Z (+/- 4/8/12/16 gauss)
Temperature in °C

Added public methods:
initialize - enable use acc, gyro (rate 952 Hz), mag (80 Hz) and set
scales: acc 16G, gyro 2000 dps and mag 16Gs.
probe - check connection over SPI by reading WHO_AM_I registers.
read_temp, read_acc, read_gyro, void read_mag - read data from
registers, after converts to SI (temperature to °C) and records this
values to arrays and variables, determined in interface.
getMotion6, getMotion9 - save acc,gyro(6) or acc,gyro,mag(9) values
in input parameters.
private:
WriteReg, ReadReg, ReadRegs - provides read/write register over SPI.
set_gyro_scale, set_acc_scale, set_mag_scale - set scale for chosen
3D sensor, which value save in gyro_scale, acc_scale and mag_scale.

List of changes:
Class became inheritor of abstract class inertial_sensor.
Inherited methods placed to public, others to private.
Deleted input parameters for initialize function.
Renamed testConnection to probe.
Deleted unused variables.
Function ReadReg no longer needs WriteData, by default it
set to 0x00.
Values of accelerometer and gyroscope convert to SI.
Changed some comments according changes.

List of changes:
Defines of registers and bits given to the table view
Remove excess spaces
Now indent = 4 spaces
Added spaces between operators
Change place of {

Using FIFO allows setting higher sample frequency and use more values for filtering.
FIFO is a 512 bytes buffer. Accelerometer and gyroscope data are written into FIFO.
This code include some additions:

 - Defines of bits for FIFO settings
 - Public methods:
   read_count_FIFO - returns count of bytes in FIFO buffer;
   enable_FIFO - enable use FIFO and record acc and gyro values to FIFO
   buffer;
   reset_FIFO - clean FIFO buffer and reset count;
   disable_FIFO - stop write acc and gyro values to FIFO buffer;
   read_FIFO - first read number of bytes in FIFO buffer,
   after that read from buffer bytes multiple sample size (12 bytes).