Refactor examples to use `np.ndarray` over `np.matrix`

[rLinks234]

numpy.matrix has been deprecated in favor of using np.ndarray (i.e., using np.array, np.asarray, etc). There are some subtle differences in behavior between the two, which makes some of the examples a bit more hairy than needed. As of the time of when this issue was filed, the pending hebi-py release (1.1.0) internally drops almost all use of np.matrix in favor of the array counterparts. No public API calls of hebi-py should longer return np.matrix; consequently, we should not be using them in the examples.

For some more info, see this stack overflow post: https://stackoverflow.com/questions/53254738/deprecation-status-of-the-numpy-matrix-class