Improve generated libstdc++ API docs

Improve generated libstdc++ API docs

	* doc/doxygen/user.cfg.in: Use EXTENSION_MAPPING tag. Add new headers
	to INPUT. Remove obsolete XML_SCHEMA and XML_DTD tags. Update
	PREDEFINED macros. Set BRIEF_MEMBER_DESC for man-pages.
	* include/backward/strstream: Correct @file comment.
	* include/bits/forward_list.h: Improve Doxygen comments.
	* include/bits/locale_facets_nonio.h: Likewise.
	* include/bits/mutex.h: Likewise.
	* include/bits/shared_ptr.h: Likewise.
	* include/bits/stl_deque.h: Likewise.
	* include/debug/vector (_Safe_vector): Add @brief section to comment.
	* include/experimental/bits/fs_dir.h: Correct @file comment.
	* include/experimental/bits/fs_fwd.h: Likewise.
	* include/experimental/bits/fs_ops.h: Likewise.
	* include/experimental/bits/fs_path.h: Likewise.
	* include/experimental/bits/string_view.tcc: Likewise.
	* include/experimental/optional: Document experimental status.
	* include/experimental/string_view: Correct @file comment.
	* include/ext/pb_ds/detail/bin_search_tree_/traits.hpp: Reduce
	whitespace to avoid Doxygen bug.
	* include/std/bitset: Remove redundant @class Doxygen command. Add
	parentheses to avoid Doxygen bug.
	* include/std/mutex: Improve Doxygen comments.
	* include/tr2/dynamic_bitset: Add missing @param documentation.
	* scripts/run_doxygen: Rename man pages for std::experimental types.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@231512 138bc75d-0d04-0410-961f-82ee72b054a4