In SPI mode, we must change the memory page depending on which register is
being read/written.
Renamed const _BME680_REG_STATUS to _BME680_REG_MEAS_STATUS to more closely
match the name in the datasheet.
Added the debug init parameter and copied the debug functionality
from the i2c class
Added the refresh_rate initi parameter
Improved the SPI class docstring
Compared the ot reference code, one expression in the lengthy calculation was split in two lines.
Since a previous interim value was used in the expression twice and replaced by the first
part of the split expression, the overall result was different to the reference code. The resulting
pressure was not that different, 10 hPa at 1000hPa absolute value, but clearly outside of the
spec with 1hPa absolute pressure error.
* The default internal attribute values for oversampling were
incorrect because they needed to be the register values, not the
human friendly ones.
* Reduce the delay after reset.
* Reduce the read delay by polling the new data bit.
* Introduce refresh_rate setting which allows for returning cached
values when the properties are accessed quickly.
* I2C writes do not auto-increment so reset the register address
for every value.
Fixes#5
