Added ring/elimination mechanic.

client/gamedata/gamedata.go

@@ -1,6 +1,14 @@
 package gamedata
 
+import "math"
+
 type Coordinates struct {
 	X float64 `json:"X"`
 	Y float64 `json:"Y"`
 }
+
+func (c Coordinates) Distance(p Coordinates) float64 {
+	dx := p.X - c.X
+	dy := p.Y - c.Y
+	return math.Sqrt(dx*dx + dy*dy)
+}