Updated to use boost/bind/bind.hpp to avoid warnings and compliance with C++20.

boost/bind.hpp emits warnings about deprecating global placeholder argument
keywords. C++20 removes std::bind1st/bind2nd, so replaced their usage with
boost::bind.

example/indirect_iterator_example.cpp

@@ -9,6 +9,7 @@
 #include <iterator>
 #include <functional>
 #include <algorithm>
+#include <boost/bind/bind.hpp>
 #include <boost/iterator/indirect_iterator.hpp>
 
 int main(int, char*[])
@@ -41,7 +42,7 @@ int main(int, char*[])
     const_indirect_last(pointers_to_chars + N);
 
   std::transform(const_indirect_first, const_indirect_last,
-                 mutable_indirect_first, std::bind1st(std::plus<char>(), 1));
+                 mutable_indirect_first, boost::bind(std::plus<char>(), 1, boost::placeholders::_1));
 
   std::copy(mutable_indirect_first, mutable_indirect_last,
             std::ostream_iterator<char>(std::cout, ","));