Add: begin shell with help command

src/libc/stdio.c

@@ -87,6 +87,9 @@ void putc(char c)
     case '\r':
       VGA_X = 0;
       break;
+    case '\t':
+      VGA_X += 4;
+      break;
     default:
       putchar(VGA_X, VGA_Y, c);
       VGA_X++;
@@ -114,6 +117,9 @@ void colorputc(char c, unsigned int color)
     case '\r':
       VGA_X = 0;
       break;
+    case '\t':
+      VGA_X += 4;
+      break;
     default:
       putchar(VGA_X, VGA_Y, c);
       putcolor(VGA_X, VGA_Y, color);

src/libc/string.c

@@ -7,3 +7,13 @@ int strlen(char* str)
   }
   return len;
 }
+
+int strcmp(char* str1, char* str2)
+{
+  while (*str1 && (*str1 == *str2))
+  {
+    str1++;
+    str2++;
+  }
+  return *(const unsigned char*)str1 - *(const unsigned char*)str2;
+}

src/libc/string.h

@@ -2,5 +2,6 @@
 #define INCLUDE_STRING_H
 
 int strlen(char* str);
+int strcmp(char* str1, char* str2);
 
 #endif