feat(repeatalpha): update subject to ask for a function instead of a program

- add main.go for exam

subjects/repeatalpha/README.md

@@ -2,25 +2,43 @@
 
 ### Instructions
 
-Write a program called `repeat_alpha` that takes a `string` and displays it repeating each alphabetical character as many times as its alphabetical index.
-
-The result must be followed by a newline (`'\n'`).
+Write a function called `RepeatAlpha` that takes a `string` and displays it repeating each alphabetical character as many times as its alphabetical index.
 
 `'a'` becomes `'a'`, `'b'` becomes `'bb'`, `'e'` becomes `'eeeee'`, etc...
 
-If the number of arguments is different from 1, the program displays nothing.
+### Expected Function
+
+```go
+func RepeatAlpha(s string) string {
+}
+```
 
 ### Usage
 
+Here is a possible program to test your function:
+
+```go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(RepeatAlpha("abc"))
+	fmt.Println(RepeatAlpha("Choumi."))
+	fmt.Println(RepeatAlpha(""))
+	fmt.Println(RepeatAlpha("abacadaba 01!"))
+}
+```
+
+And its output:
+
 ```console
-$ go run . abc | cat -e
-abbccc
-$ go run . Choumi. | cat -e
+$ go run . | cat -e
+abbccc$
 CCChhhhhhhhooooooooooooooouuuuuuuuuuuuuuuuuuuuummmmmmmmmmmmmiiiiiiiii.$
-$ go run . "abacadaba 01!" | cat -e
-abbacccaddddabba 01!$
-$ go run .
-$ go run . "" | cat -e
 $
+abbacccaddddabba 01!$
 $
 ```

subjects/repeatalpha/main.go

@@ -0,0 +1,12 @@
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(RepeatAlpha("abc"))
+	fmt.Println(RepeatAlpha("Choumi."))
+	fmt.Println(RepeatAlpha(""))
+	fmt.Println(RepeatAlpha("abacadaba 01!"))
+}