Big Update

Added crosshairs; when enabled, the game locks the cursor to the center
so that the control is centered on the crosshair; you can generate an
object in the middle of a grid object at the crosshair on click; you
can select which obect you will create by clicking on it; you can shoot
a soccer ball with a right click; added multiple new terrains and
textures; experimented with tree builder; added frames per second
calculation and display