Add support for strings (func serial_print) and newlines in serial

kernel/kernel/kernel.c

@@ -10,6 +10,9 @@ void kernel_main(void) {
 	printf("Hello from OrionOS!\n");
 	printf("Testing serial\n");
 	init_serial();
-	write_serial('t');
+	serial_print("Test is success!\n");
+	serial_print("Newline test\n");
+	serial_print("No newline test ");
+	serial_print("No newline test");
 	printf("Test finished success!\n");
 }

kernel/kernel/serial.h

@@ -1,4 +1,5 @@
 #include <stdint.h>
+#include <string.h>
 
 #define PORT 0x3f8          // COM1
  
@@ -44,8 +45,16 @@ void write_serial(char a) {
    outb(PORT, a);
 }
 
-void serial_printf() {
-
+void serial_print(const char* str, ...) {
+  size_t len = strlen(str);
+  for (size_t i=0; i < len; i++) {
+    if (str[i] == '\n') {
+	write_serial('\r');
+	write_serial('\n');
+    } else {
+      write_serial(str[i]);
+    }
+  }
 }
 
 inline void outb(uint16_t port, uint8_t val)