features removed

as adviced by
  rustc --explain E0557

src/lib.rs

@@ -1,10 +1,8 @@
 //! Definitions of register addresses and bits within those registers
 
 #![feature(llvm_asm)]
-#![feature(const_fn)]
 #![feature(associated_type_defaults)]
 #![feature(lang_items)]
-#![feature(unwind_attributes)]
 #![feature(proc_macro_hygiene)]
 
 #![no_std]