Extract & Epoch functions about spiketools

[TomDonoghue]

Following #177, the functionality to get time / position a player is closest to an object is now supported by get_closet_position.

For example, assume we have ptimes, pos, and obj_loc, one can do the following:

closest_ind = get_closest_position(pos, obj_loc)
closest_time = ptimes[closest_ind]

This seems to address the main topic here, and while the new function does practically the same thing as get_ind_by_time, there is now no need to change any descriptions related to this. Because of this, I'm going to close this now.