Improve kernel logging

Current function name is automatically prepended to all log entries.
Helper macros added to log local variables.

src/kernel/kernel.c

@@ -30,7 +30,7 @@ __attribute__((interrupt)) void isr_page_fault(__attribute__((unused)) struct in
   __asm__ volatile("mov %%cr2, %0" : "=r"(cr2));
 
   char msg[80];
-  string_format("EXCEPTION: page fault; addr=%x err=%x", 80, msg, cr2, error_code);
+  string_format("EXCEPTION: page fault; addr=%lx err=%lx", 80, msg, cr2, error_code);
 
   vga_set_string(VGA_HEIGHT - 1, 0, msg, 0x4F);
   while (1)