Add: serial logging function w/ errlevels

kmain.c

@@ -3,11 +3,12 @@
 
 int kmain(int retvalue)
 {
+  init_serial();
+  log("serial connection established", 3);
+  log("Kernel started", 2);
+
   clear();
   puts("hello\nbrave\nnew\nworld");
 
-  init_serial();
-  serial_puts("Hello, brave new world. This is a message to let you know that the kernel has started.\n");
-  serial_puts("This is a second message.\n");
   return retvalue;
 }

serial.c

@@ -42,3 +42,24 @@ void serial_puts(const char* str)
     write_serial(str[i]);
   }
 }
+
+void log(const char* str, const int errlevel)
+{
+  switch (errlevel)
+  {
+    case 0:
+      serial_puts("[ERROR] ");
+      break;
+    case 1:
+      serial_puts("[WARNING] ");
+      break;
+    case 2:
+      serial_puts("[INFO] ");
+      break;
+    case 3:
+      serial_puts("[DEBUG] ");
+      break;
+  }
+  serial_puts(str);
+  serial_puts("\n");
+}

serial.h

@@ -7,5 +7,6 @@ int init_serial();
 int is_transmit_empty();
 void write_serial(const char a);
 void serial_puts(const char* str);
+void log(const char* str, const int errlevel);
 
 #endif