Use single dataReady() method, instead of accelDataReady/gyroDataReady

[eriknyquist]

This method is a bit more flexible. There is a version with no
parameters, which will return true if all enabled sensors have new
data. There is one overload, that takes a single 'flags' parameter,
which returns true if all enabled and selected sensors have new data.
Sensors are selectable through pre-defined bit flags. For example;

CurieIMU.dataReady() : this will return true if both the accel and gyro
are enabled, and both have new data ready.

CurieIMU.dataReady(ACCEL | GYRO) : this will return true if both the
accel and gyro have new data ready (if one of the passed sensors is not
enabled, it is ignored and the function will behave as if that sensor was not
specified)

CurieIMU.dataReady(GYRO) : this will return true if the gyro is
enabled and has new data ready.

CurieIMU.dataReady(ACCEL) : this will return true if the accel is
enabled and has new data ready.

This also involved changing the 'begin' method to allow selective
enabling of sensors, e.g.

CurieIMU.begin() : same as it always has, initializes IMU, enabling
both accel and gyro

CurieIMU.begin(ACCEL | GYRO) : initializes IMU, enabling both accel
and gyro

CurieIMU.begin(ACCEL) : initializes IMU, enabling accel only

CurieIMU.begin(GYRO) : initializes IMU, enabling  gyro only

[eriknyquist]

@russmcinnis to verify

[PaulStoffregen]

Just curious, why dataReady?

In the Arduino world, isn't the well established convention to name this "available"?

[eriknyquist]

dataReady() because it does what it says on the tin..... available generally tells you how many buffered incoming items are available. dataReady() just tells you whether the next un-read sample is available from a particular sensor, no buffering. True or false.

[eriknyquist]

@PaulStoffregen also, @facchinm and @tigoe and I discussed this back and forth for a bit, and this API is the one we all agreed on :)