Implemented lots of new functions

photon/libc/string/strdup.c

@@ -0,0 +1,11 @@
+#include <string.h>
+#include <stdlib.h>
+
+char *strdup(const char *str)
+{
+    size_t len = strlen(str);
+    char *out = malloc(len + 1);
+    memcpy(out, str, len);
+    out[len] = 0;
+    return out;
+}