implemented fun makeAbbr()

Author: IrynaKhrustalova

src/main/kotlin/mate/academy/MakeAbbreviation.kt

@@ -1,6 +1,16 @@
 package mate.academy
 
+const val ONE = 1
+
 fun makeAbbr(source: String) : String {
-    // implement this function
-    return ""
+    val result = mutableListOf<Char>()
+    result.add(source.first())
+    source.forEachIndexed { i, c ->
+        if (c == ' ') {
+            result.add(source[i + ONE])
+        }
+    }
+    return result.toString()
+        .replace(Regex("[^A-Za-z]"), "")
+        .uppercase()
 }