Fix formatting in documentation of ffi::CString

Author: dirk

src/libstd/ffi/c_str.rs

@@ -219,10 +219,10 @@ impl CString {
         CString { inner: v.into_boxed_slice() }
     }
 
-    /// Retakes ownership of a CString that was transferred to C.
+    /// Retakes ownership of a `CString` that was transferred to C.
     ///
     /// This should only ever be called with a pointer that was earlier
-    /// obtained by calling `into_raw` on a CString. Additionally, the length
+    /// obtained by calling `into_raw` on a `CString`. Additionally, the length
     /// of the string will be recalculated from the pointer.
     #[stable(feature = "cstr_memory", since = "1.4.0")]
     pub unsafe fn from_raw(ptr: *mut c_char) -> CString {