BOOST_DEPRECATED can be used to mark functions, types and objects as
deprecated, with a message with a recommendation of replacement. Using
such marked symbols in code will generate compiler warnings, with the
specified message, if possible.
The warnings can be suppressed if BOOST_ALLOW_DEPRECATED_SYMBOLS is defined.
Additionally, added support BOOST_ALLOW_DEPRECATED macro that not only
allows for deprecated symbols but also deprecated headers (i.e. defining
BOOST_ALLOW_DEPRECATED is equivalent to defining both
BOOST_ALLOW_DEPRECATED_SYMBOLS and BOOST_ALLOW_DEPRECATED_HEADERS).
