Added reset button

-Press "r" to reset the map; generates a new map
-currently having memory leaks, i think its something to do with drawing
new hexes with rivers on it. Should not happen if there is no reset
-fixed river generation sometimes getting stuck in an infinite loop; it
now fails the generation if it didnt generate a correct river after 10+
trys
-added instructions to the game (As of sept 9, 2014)