Merge branch 'aj_pow' into debug

services/math_engine.go

@@ -15,4 +15,10 @@ func init() {
 	engine.RegFunction("ln", 1, func(expr ...engine.ExprAST) float64 {
 		return math.Log(engine.ExprASTResult(expr[0]))
 	})
+
+	engine.RegFunction("pow", 2, func(expr ...engine.ExprAST) float64 {
+		x := engine.ExprASTResult(expr[0])
+		y := engine.ExprASTResult(expr[1])
+		return math.Pow(x, y)
+	})
 }