move out most of text

see https://github.com/rust-embedded/book/pull/20

examples/panic.rs

@@ -1,44 +1,28 @@
-//! Changing the panic handler
+//! Changing the panicking behavior
 //!
-//! The easiest way to change the panic handler is to use a different [panic handler crate][0].
+//! The easiest way to change the panicking behavior is to use a different [panic handler crate][0].
 //!
 //! [0]: https://crates.io/keywords/panic-impl
-//!
-//! ---
 
 #![no_main]
 #![no_std]
 
-#[macro_use]
-extern crate cortex_m_rt as rt;
+// Pick one of these panic handlers:
 
-// Pick one of these two panic handlers:
+// `panic!` halts execution; the panic message is ignored
+extern crate panic_halt;
 
 // Reports panic messages to the host stderr using semihosting
-extern crate panic_semihosting;
+// NOTE to use this you need to uncomment the `panic-semihosting` dependency in Cargo.toml
+// extern crate panic_semihosting;
 
 // Logs panic messages using the ITM (Instrumentation Trace Macrocell)
 // NOTE to use this you need to uncomment the `panic-itm` dependency in Cargo.toml
 // extern crate panic_itm;
 
-use rt::ExceptionFrame;
-
-entry!(main);
+use cortex_m_rt::entry;
 
+#[entry]
 fn main() -> ! {
     panic!("Oops")
 }
-
-// define the hard fault handler
-exception!(HardFault, hard_fault);
-
-fn hard_fault(ef: &ExceptionFrame) -> ! {
-    panic!("HardFault at {:#?}", ef);
-}
-
-// define the default exception handler
-exception!(*, default_handler);
-
-fn default_handler(irqn: i16) {
-    panic!("Unhandled exception (IRQn = {})", irqn);
-}