Remove "extern crate" in favor "use"

Author: Sh3Rm4n

examples/pwm.rs

@@ -3,7 +3,7 @@
 #![no_std]
 #![no_main]
 
-extern crate panic_semihosting;
+use panic_semihosting as _;
 
 use cortex_m_rt::entry;
 //use cortex_m_semihosting::hprintln;

examples/spi.rs

@@ -3,7 +3,7 @@
 #![no_std]
 #![no_main]
 
-extern crate panic_semihosting;
+use panic_semihosting as _;
 
 use stm32f3xx_hal as hal;
 

examples/toggle.rs

@@ -6,7 +6,7 @@
 #![no_main]
 #![no_std]
 
-extern crate panic_semihosting;
+use panic_semihosting as _;
 
 use cortex_m_rt::entry;
 use stm32f3xx_hal::prelude::*;

examples/usb_serial.rs

@@ -3,7 +3,7 @@
 #![no_std]
 #![no_main]
 
-extern crate panic_semihosting;
+use panic_semihosting as _;
 
 use cortex_m::asm::delay;
 use cortex_m_rt::entry;