Set fall distance to 0, if the player could fly or is in creative mode.
[BLEEDING] Maintain location traces (not making use of those, yet).

No change for the function of the plugin, except if there are new bugs.
Actual changes:
* Keep track of squared distance to the previous element in a trace.
* Balance mergeDist: prevent merging the latest entry, if the squared
	distance from the latest to the second latest element is greater
	than mergeDist. Never merge if there are only two entries in total.
* Add convenience methods for resetting and updating the trace.
* Maintain the moving traces actively. With intended use being
	player-player interaction, we will not reset with every teleport.