Add support for libstrophe-0.13 and 0.14

Author: twistedfall

src/alloc_context.rs

@@ -1,7 +1,8 @@
-use std::ffi::c_void;
-use std::mem::{align_of, size_of};
-use std::ptr::NonNull;
-use std::{alloc, ptr};
+use core::ffi::c_void;
+use core::mem::{align_of, size_of};
+use core::ptr;
+use core::ptr::NonNull;
+use std::alloc;
 
 /// Internal `Context` that only specifies allocation functions and uses null logger. Needed to not pass
 /// `Context` to e.g. `Stanza` because it uses only allocation functions from `Context`.