Add First() and Last() in chain operation (#183)

This also improves example in the README

README.md

@@ -49,7 +49,7 @@ Or, if you need to chain multiple operations you can use one of:
 - [`pie.OfOrdered`](https://pkg.go.dev/github.com/elliotchance/pie/v2#OfOrdered) - only works with numbers and strings, but has more functions.
 - [`pie.OfNumeric`](https://pkg.go.dev/github.com/elliotchance/pie/v2#OfNumeric) - only works with numbers, but has all functions.
 
-[Run this program](https://go.dev/play/p/cDLBYzKJ9ld)
+[Run this program](https://go.dev/play/p/4IhVbw0koxg)
 
 ```go
 package main
@@ -67,7 +67,7 @@ func main() {
             return strings.HasPrefix(name, "J")
         }).
         Map(strings.ToUpper).
-        LastOr("")
+        Last()
 
     fmt.Println(name) // "SALLY"
 }

v2/of.go

@@ -49,6 +49,10 @@ func (o OfSlice[T]) FindFirstUsing(fn func(value T) bool) int {
 	return FindFirstUsing(o.Result, fn)
 }
 
+func (o OfSlice[T]) First() T {
+	return First(o.Result)
+}
+
 func (o OfSlice[T]) FirstOr(defaultValue T) T {
 	return FirstOr(o.Result, defaultValue)
 }
@@ -57,6 +61,10 @@ func (o OfSlice[T]) Insert(index int, values ...T) OfSlice[T] {
 	return OfSlice[T]{Insert(o.Result, index, values...)}
 }
 
+func (o OfSlice[T]) Last() T {
+	return Last(o.Result)
+}
+
 func (o OfSlice[T]) LastOr(defaultValue T) T {
 	return LastOr(o.Result, defaultValue)
 }

v2/of_numeric.go

@@ -80,6 +80,10 @@ func (o OfNumericSlice[T]) FindFirstUsing(fn func(value T) bool) int {
 	return FindFirstUsing(o.Result, fn)
 }
 
+func (o OfNumericSlice[T]) First() T {
+	return First(o.Result)
+}
+
 func (o OfNumericSlice[T]) FirstOr(defaultValue T) T {
 	return FirstOr(o.Result, defaultValue)
 }
@@ -124,6 +128,10 @@ func (o OfNumericSlice[T]) JSONStringIndent(prefix, indent string) string {
 	return JSONStringIndent(o.Result, prefix, indent)
 }
 
+func (o OfNumericSlice[T]) Last() T {
+	return Last(o.Result)
+}
+
 func (o OfNumericSlice[T]) LastOr(defaultValue T) T {
 	return LastOr(o.Result, defaultValue)
 }

v2/of_ordered.go

@@ -76,6 +76,10 @@ func (o OfOrderedSlice[T]) FindFirstUsing(fn func(value T) bool) int {
 	return FindFirstUsing(o.Result, fn)
 }
 
+func (o OfOrderedSlice[T]) First() T {
+	return First(o.Result)
+}
+
 func (o OfOrderedSlice[T]) FirstOr(defaultValue T) T {
 	return FirstOr(o.Result, defaultValue)
 }
@@ -120,6 +124,10 @@ func (o OfOrderedSlice[T]) JSONStringIndent(prefix, indent string) string {
 	return JSONStringIndent(o.Result, prefix, indent)
 }
 
+func (o OfOrderedSlice[T]) Last() T {
+	return Last(o.Result)
+}
+
 func (o OfOrderedSlice[T]) LastOr(defaultValue T) T {
 	return LastOr(o.Result, defaultValue)
 }