moved string stuff to it's own file

src/main.rs

@@ -1,3 +1,4 @@
+mod string;
 mod fmt_debug;
 
 // when a String is passed to this function a move occurs:
@@ -41,6 +42,7 @@ fn _get_static_str() -> &'static str {
 }
 
 fn main() {
+    println!("Hello, world!");
     fmt_debug::test_report();
 
     let s = String::new(); // no heap allocation until we add characters (capacity > 0)
@@ -78,6 +80,4 @@ fn main() {
     let _s6 = String::from(s_lit); //underlying data copied to heap
 
     // todo: Cow
-
-    println!("Hello, world!");
 }