feat: completed solutions

.rustlings-state.txt

@@ -1,6 +1,6 @@
 DON'T EDIT THIS FILE!
 
-structs1
+as_ref_mut
 
 intro1
 intro2
@@ -31,4 +31,68 @@ move_semantics1
 move_semantics2
 move_semantics3
 move_semantics4
-move_semantics5
+move_semantics5
+structs1
+structs2
+structs3
+enums1
+enums2
+enums3
+strings1
+strings2
+strings3
+strings4
+modules1
+modules2
+modules3
+hashmaps1
+hashmaps2
+hashmaps3
+quiz2
+options1
+options2
+options3
+errors1
+errors2
+errors3
+errors4
+errors5
+errors6
+generics1
+generics2
+traits1
+traits2
+traits3
+traits4
+traits5
+quiz3
+lifetimes1
+lifetimes2
+lifetimes3
+tests1
+tests2
+tests3
+iterators1
+iterators2
+iterators3
+iterators4
+iterators5
+box1
+rc1
+arc1
+cow1
+threads1
+threads2
+threads3
+macros1
+macros2
+macros3
+macros4
+clippy1
+clippy2
+clippy3
+using_as
+from_into
+from_str
+try_from_into
+as_ref_mut