Transpose array allocation in add_vector_property() (in population.py)

[clorton]

Probably doesn't have any measurable performance impact, but the current specification of dimensions in array allocation means that the most likely access pattern does not access contiguous locations in memory.

Also, property[tick, :] might be a little more sensible than property[:, tick] from an API perspective.

This would be a breaking change.

[krosenfeld-IDM]

hi @clorton