Div on CPU (#58)

* Added Div on CPU

* Removed eps. value

* Fixed tabs

tinygrad/ops.py

@@ -36,6 +36,18 @@ class Mul(Function):
     return y*grad_output, x*grad_output
 register('mul', Mul)
 
+class Div(Function):
+  @staticmethod
+  def forward(ctx, x, y):
+    ctx.save_for_backward(x, y)
+    return x / y
+
+  @staticmethod
+  def backward(ctx, grad_output):
+    x,y = ctx.saved_tensors
+    return grad_output / y, -x * grad_output / y**2
+register('div', Div)
+
 class Pow(Function):
   @staticmethod
   def forward(ctx, x, y):