move out most of text

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

examples/crash.rs

@@ -79,36 +79,18 @@
 #![no_main]
 #![no_std]
 
-extern crate cortex_m;
-#[macro_use]
-extern crate cortex_m_rt as rt;
-extern crate panic_semihosting;
+extern crate panic_halt;
 
 use core::ptr;
 
-use rt::ExceptionFrame;
-
-entry!(main);
+use cortex_m_rt::entry;
 
+#[entry]
 fn main() -> ! {
     unsafe {
-        // read an address outside of the RAM region; causes a HardFault exception
+        // read an address outside of the RAM region; this causes a HardFault exception
         ptr::read_volatile(0x2FFF_FFFF as *const u32);
     }
 
     loop {}
 }
-
-// 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);
-}