Add in-cell aiming

[AChorostian]

I suggest mapping one cell, like in this sketch. (additional lines just show how hexagon area should be interpreted)

This will let a user shot another cell on the map.

[malinowskikam]

Tile's get_angle() method can be used to aim the artillery. We can use this to calculate exact pixel which got hit, and handle it similar to mouse event to get which tile got hit.