[#1] Updated the library to compile for Rust 2021.

This was mostly an issue of changing the way Trait objects were
implemented now that you are supposed to use the dyn keyword.

Also changed some atomic operations to use the new non-deprecated
functions.

examples/logger.rs

@@ -60,7 +60,7 @@ impl TestLogger
    }
 
    #[cfg(not(feature="use_std"))]
-   fn set_logger() -> *const Logger
+   fn set_logger() -> *const dyn Logger
    {
       &CORE_LOGGER
    }