Added fclose_deleter.

fclose_deleter can be used as a deleter function object for std::FILE
pointers returned by std::fopen.

doc/core.qbk

@@ -60,6 +60,7 @@ criteria for inclusion is that the utility component be:
 [include noinit_adaptor.qbk]
 [include noncopyable.qbk]
 [include null_deleter.qbk]
+[include fclose_deleter.qbk]
 [include nvp.qbk]
 [include pointer_traits.qbk]
 [include quick_exit.qbk]

doc/fclose_deleter.qbk

@@ -0,0 +1,34 @@
+[/
+ / Copyright (c) 2022 Andrey Semashev
+ /
+ / Distributed under the Boost Software License, Version 1.0. (See accompanying
+ / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ /]
+
+[section:fclose_deleter fclose_deleter]
+
+[simplesect Authors]
+
+* Andrey Semashev
+
+[endsimplesect]
+
+[section Header <boost/core/fclose_deleter.hpp>]
+
+The header `<boost/core/fclose_deleter.hpp>` defines the `boost::fclose_deleter` function object,
+which can be used as a deleter with smart pointers such as `unique_ptr` or `shared_ptr` pointing to `std::FILE`.
+structures returned by `std::fopen` calls. The deleter calls `std::fclose` on the passed pointer, causing
+the file stream to be flushed and closed.
+
+[section Example]
+``
+std::unique_ptr< std::FILE, boost::fclose_deleter > make_file(const char* filename, const char* open_mode)
+{
+    return { std::fopen(filename, open_mode) };
+}
+``
+[endsect]
+
+[endsect]
+
+[endsect]