added shell module, with some trig functions

src/robotwar/shell.clj

@@ -0,0 +1,25 @@
+(ns robotwar.shell
+  (:use [robotwar.constants]))
+
+
+(defn deg->rad
+  [angle]
+  (* angle (/ Math/PI 180)))
+
+(defn decompose-angle
+  [angle]
+  {:x (Math/cos angle)
+   :y (Math/sin angle)}) 
+
+(defn new-shell
+  [pos-x pos-y aim distance]
+  ; TODO: make the starting point dependent upon the robot radius,
+  ; which should be in constants.
+  (let [{unit-x :x unit-y :y} (decompose-angle (deg->rad aim))] 
+    {:pos-x pos-x
+     :pos-y pos-y
+     :v-x (* unit-x SHELL-SPEED)
+     :v-y (* unit-y SHELL-SPEED)
+     :dest-x (* unit-x distance)
+     :dest-y (* unit-y distance)})) 
+