Visually align registers & show 16 bytes for each

This change right-aligns the register names in the output of the "regs" command,
and pads out the display of the hex value of each register to 16 bytes. This
makes scanning registers for set values a bit easier.

proc/registers_darwin_amd64.go

@@ -62,7 +62,7 @@ func (r *Regs) String() string {
 		{"Gs_base", r.gs_base},
 	}
 	for _, reg := range regs {
-		fmt.Fprintf(&buf, "%s = 0x%x\n", reg.k, reg.v)
+		fmt.Fprintf(&buf, "%8s = %0#16x\n", reg.k, reg.v)
 	}
 	return buf.String()
 }

proc/registers_linux_amd64.go

@@ -43,7 +43,7 @@ func (r *Regs) String() string {
 		{"Gs", r.regs.Gs},
 	}
 	for _, reg := range regs {
-		fmt.Fprintf(&buf, "%s = 0x%x\n", reg.k, reg.v)
+		fmt.Fprintf(&buf, "%8s = %0#16x\n", reg.k, reg.v)
 	}
 	return buf.String()
 }