Implement strpbrk(), add strpbrk test

tests/string/strpbrk.c

@@ -0,0 +1,21 @@
+#include <string.h>
+#include <stdio.h>
+
+int main(int argc, char* argv[]) {
+    char* str = "The quick drawn fix jumps over the lazy bug";
+
+    // should be "The quick drawn fix jumps over the lazy bug"
+    char* str1 = strpbrk(str, "From The Very Beginning");
+    printf("%s\n", (str1) ? str1 : "NULL"); 
+
+    // should be "lazy bug"
+    char* str2 = strpbrk(str, "lzbg");
+    printf("%s\n", (str2) ? str2 : "NULL"); 
+
+
+    // should be "NULL"
+    char* str3 = strpbrk(str, "404");
+    printf("%s\n", (str3) ? str3 : "NULL"); 
+
+    return 0;
+}