Add mathutil package and constants

Introduce a new package for math utilities, including an Add function
and Euler's number. Also, add constants for Celsius conversion and basic
arithmetic.

main.go

@@ -2,8 +2,40 @@ package main
 
 import (
 	"fmt"
+	"curso-goland/mathutil"
+	"math"
+)
+
+const GrauCelsius = 273.15
+
+const (
+	A = 1
+	B = 2
 )
 
 func main() {
 	fmt.Println("Hello, World!")
+
+	fmt.Println(mathutil.Add(1, 2))
+
+	fmt.Println(math.Sqrt(144))
+
+	var x int = 10
+	x = x + 1
+	fmt.Println(x)
+
+	var a, b int = 1, 2
+	c := a + b
+	fmt.Println(c)
+
+	nombre, edad := "Juan", 30
+	fmt.Println(nombre, edad)
+
+	fmt.Println(mathutil.EulersNumber)
+
+	fmt.Println(math.Pi)
+
+	fmt.Println(GrauCelsius)
+
+	fmt.Println(A + B)
 }