Release v3.3.0b4

Fixed

• Fixed gyro on Technic Hub occasionally giving a bad value, which made it
  not calibrate properly (support#1026).
• Fixed discrepancy in heading value across hubs by accounting for sampling
  time (support#1022).
• Fixed iterator for Matrix objects giving bad values.
• Fixed Bluetooth sometimes locking up on Technic/City hubs (support#567).
• Fixed GyroDriveBase being slow to respond to heading perturbations when
  driving at high speed (support#1032).

Added

• Added pybricks.tools.cross(a, b) to get a vector cross product.
• Added experimental implementation of hub.imu.heading() ([support#912]).
• Added support for reading single-axis rotation, which is useful in
  applications like balancing robots, where full 3D orientation is not
  required, or even undesired.
• Added hub.imu.ready() to check that the IMU has been calibrated and is
  ready for use.
• Added GyroDriveBase class to control drivebase steering with the gyro.
• Added optional window parameter to Motor.speed to specify the
  differentiation window size that determines the average speed. This lets the
  user choose smaller values to get a more responsive (but noisier) or higher
  values to get a smoother (but more delayed) speed signal.

Removed

• Removed positive_direction from DriveBase initializer. This was
  temporarily added in the previous beta release to facilitate gyro support,
  but made it more complicated than needed (support#992).
• Removed pybricks.geometry in an effort to reduce the number of modules with
  just a few elements. Matrix and vector have moved to tools. The Axis
  enum was moved to parameters. Each item can still be imported from its
  original location for backwards compatibility.