Add Val() method. (#10)

* Add Val() method.

Usecases:
- Custom serialization / deserialization
- Persisting Amount as two columns in a database

* Rename Val() to Scaled().

Co-authored-by: Nikolay Dubina <nikolay.dubina.pub@gmail.com>
Signed-off-by: Michael Würtinger <michael@wuertinger.de>

* Add TestScaled.

* Rename package back to fpmoney_test.

* Turn test into examples.

Co-authored-by: Nikolay Dubina <nikolay.dubina.pub@gmail.com>
Signed-off-by: Michael Würtinger <michael@wuertinger.de>

---------

Signed-off-by: Michael Würtinger <michael@wuertinger.de>
Co-authored-by: Nikolay Dubina <nikolay.dubina.pub@gmail.com>

amount.go

@@ -35,6 +35,8 @@ func (a Amount) Float64() float64 { return float64(a.v) / float64(a.c.scale()) }
 
 func (a Amount) Currency() Currency { return a.c }
 
+func (a Amount) Scaled() int64 { return a.v }
+
 func (a Amount) Add(b Amount) Amount {
 	checkCurrency(a.c, b.c)
 	return Amount{v: a.v + b.v, c: a.c}

amount_test.go

@@ -76,6 +76,35 @@ func ExampleFromFloat() {
 	// Output: 144.96 SGD
 }
 
+func ExampleAmount_Scaled_fractions() {
+	v := fpmoney.FromFloat(42.23, fpmoney.EUR)
+	fmt.Println(v.Scaled())
+	// Output: 4223
+}
+
+func ExampleAmount_Scaled_many_fractions() {
+	v := fpmoney.FromFloat(17.0, fpmoney.CLF)
+	fmt.Println(v.Scaled())
+	// Output: 170000
+}
+
+func ExampleAmount_Scaled_large() {
+	v := fpmoney.FromFloat(8764534896.42, fpmoney.USD)
+	fmt.Println(v.Scaled())
+	// Output: 876453489642
+}
+func ExampleAmount_Scaled_whole() {
+	v := fpmoney.FromFloat(23.0, fpmoney.EUR)
+	fmt.Println(v.Scaled())
+	// Output: 2300
+}
+
+func ExampleAmount_Scaled_from_scaled() {
+	v := fpmoney.FromIntScaled(17, fpmoney.EUR)
+	fmt.Println(v.Scaled())
+	// Output: 17
+}
+
 func FuzzArithmetics(f *testing.F) {
 	currencies := [...]fpmoney.Currency{
 		fpmoney.KRW,