add module system and move sensor into core with it

src/lib.rs

@@ -1,10 +1,9 @@
 #![feature(macro_metavar_expr_concat)]
 #![feature(const_ops)]
 #![feature(const_trait_impl)]
-#![feature(const_from)]
+#![feature(const_convert)]
 #![feature(map_try_insert)]
 #![feature(trait_alias)]
-#![feature(round_char_boundary)]
 #![feature(unboxed_closures)]
 #![feature(fn_traits)]