feat(config)!: Device creation function is now named entry

It now has to be called 'setup', this makes it possible to just
include the table as a whole in devices and it will automatically call
the correct function.

src/lib.rs

@@ -1,3 +1,5 @@
+#![feature(if_let_guard)]
+
 pub mod config;
 pub mod schedule;
 pub mod secret;