Support Quantity-like annotations when saving/loading .mat files

[mdenker]

Currently, the neomatlabio can save annotations of objects. If these annotations are a quantities object, they loose their units and only a classic np.array is retained. In contrast, object properties (e.g., .t_start) are saved as two annotations containing value and unit of a quantities object. This behavior of properties should be mirrored for annotations that are quantities objects.

To reproduce and test, add an annotation

yop=[3, 4, 5] * pq.ms

to test_write_read_single_spike in test_neomatlabio.py.

Related to #633

[samuelgarcia]

The miletones of 0.10.0 is a good choice :wink: