Remove assembly forcing stack.

Fixes #51

There should be no reason for manually trying to load the stack.  Cortex
devices can be programmed with only C, and any code that needed this
would indicate broken vectors.

lib/cm3/vector.c

@@ -67,8 +67,6 @@ void WEAK __attribute__ ((naked)) reset_handler(void)
 {
 	volatile unsigned *src, *dest;
 
-	__asm__("MSR msp, %0" : : "r"(&_stack));
-
 	for (src = &_data_loadaddr, dest = &_data; dest < &_edata; src++, dest++)
 		*dest = *src;