Move headers to core; add quickbook documentation

doc/explicit_operator_bool.qbk

@@ -1,3 +1,5 @@
+[section:explicit_operator_bool Header <boost/core/explicit_operator_bool.hpp>]
+
 [/
  / Copyright (c) 2013 Andrey Semashev
  /
@@ -5,17 +7,6 @@
  / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  /]
 
-[article BOOST_EXPLICIT_OPERATOR_BOOL, BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT and BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL
-    [quickbook 1.5]
-    [authors [Semashev, Andrey]]
-    [copyright 2013 Andrey Semashev]
-    [license
-        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 Overview]
 [/===============]
@@ -24,7 +15,6 @@
 
 [endsect]
 
-
 [/===============]
 [section Examples]
 [/===============]
@@ -62,3 +52,5 @@ Now `my_ptr` can be used in conditional expressions, similarly to a regular poin
 * The macro was extracted from Boost.Log.
 
 [endsect]
+
+[endsect]