Merge pull request below#42 from skrrb/fix-entrypoint

Author: below

Chapter 01/HelloWorld.s

@@ -6,12 +6,12 @@
 // X16 - Mach System Call function number
 //
 
-.global start			// Provide program starting address to linker
+.global _start			// Provide program starting address to linker
 .align 2			// Make sure everything is aligned properly
 
 // Setup the parameters to print hello world
 // and then call the Kernel to do it.
-start: mov	X0, #1		// 1 = StdOut
+_start: mov	X0, #1		// 1 = StdOut
 	adr	X1, helloworld 	// string to print
 	mov	X2, #13	    	// length of our string
 	mov	X16, #4		// Unix write system call