Explicitly set the SPI clock to operate at 4MHz

The ADXL362's SPI clock can operate in the range of [1MHz, 5MHz]
so using the SPI classes setClockDivider method, we pick a rate
in the middle of that range.

Signed-off-by: ZachWick <zach@zachwick.com>
ADXL362::read[i]Data methods now return the read data

These methods for reading just the X, Y, Z, and Temperature
registers were not actually returning any read data. They only
printed the read data out if debugSerial was true.

Signed-off-by: ZachWick <zach@zachwick.com>
Adds methods to read only the Most Significant Byte registers for X,Y,Z

The ADXL362 has dedicated registers that only have the most significant byte
of X-axis, Y-axis, and Z-axis data. These methods expose a simple way to read
these registers.

Signed-off-by: ZachWick <zach@zachwick.com>
Adds the "include_sx_bits" parameter to the read[X,Y,Z]Data methods

The "sign extension" bits are the most significant four bits. These
bits are always the same as the most significant bit of the 12bits of
data per axis.
Leaving the sign extension bits in the returned value is prone to
data misinterpretation.

Signed-off-by: ZachWick <zach@zachwick.com>
The readXYZTData() method now returns values by reference and has include_sx_bits flag

This makes the readXYZTData method consistent with the other read methods.

Signed-off-by: ZachWick <zach@zachwick.com>
Adds the include_sx_bits flag to the readTemp method

This change brings the readTemp method into line with the other read methods.

Signed-off-by: ZachWick <zach@zachwick.com>