Get nyancat nyanning in Serenity.

I found a cute program that renders an animated nyancat in the terminal.
This patch adds enough hackery to get it working correctly. :^)

LibC/string.cpp

@@ -5,6 +5,7 @@
 #include <assert.h>
 #include <stdlib.h>
 #include <AK/Types.h>
+#include <AK/StdLibExtras.h>
 
 extern "C" {
 
@@ -60,6 +61,15 @@ char* strdup(const char* str)
     return new_str;
 }
 
+char* strndup(const char* str, size_t maxlen)
+{
+    size_t len = min(strlen(str), maxlen);
+    char* new_str = (char*)malloc(len + 1);
+    memcpy(new_str, str, len);
+    new_str[len] = 0;
+    return new_str;
+}
+
 int strcmp(const char* s1, const char* s2)
 {
     while (*s1 == *s2++)