Add Polymorphic Memory Resource utilities and rework the separately compiled library:

- Dlmalloc's based C function are boost_cont_xxx no longer exported, but wrapped into C++ linkage dlmalloc_xxx functions to effectively reuse Boost's dynamic library and autolink machinery instead of rewriting machinery to compile the C source file.
- Refactored scoped_allocator_adaptor's construct logic as it was shared with polymorphic allocator's one. Moved common logic to detail/dispatch_uses_allocator.hpp. Refactored also scoped_allocator_adaptor test utilities to be reused with polymorphic_allocator tests.

example/doc_pmr.cpp

@@ -0,0 +1,97 @@
+//////////////////////////////////////////////////////////////////////////////
+//
+// (C) Copyright Ion Gaztanaga 2015-2015. 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)
+//
+// See http://www.boost.org/libs/container for documentation.
+//
+//////////////////////////////////////////////////////////////////////////////
+//[doc_pmr_ShoppingList_hpp
+//ShoppingList.hpp
+#include <boost/container/pmr/vector.hpp>
+#include <boost/container/pmr/string.hpp>
+
+class ShoppingList
+{
+   // A vector of strings using polymorphic allocators. Every element
+   // of the vector will use the same allocator as the vector itself.
+   boost::container::pmr::vector_of
+      <boost::container::pmr::string>::type m_strvec;
+   //Alternatively in compilers that support template aliases:
+   //    boost::container::pmr::vector<boost::container::pmr::string> m_strvec;
+   public:
+
+   // This makes uses_allocator<ShoppingList, memory_resource*>::value true
+   typedef boost::container::pmr::memory_resource* allocator_type;
+
+   // If the allocator is not specified, "m_strvec" uses pmr::get_default_resource().
+   explicit ShoppingList(allocator_type alloc = 0)
+      : m_strvec(alloc) {}
+
+   // Copy constructor. As allocator is not specified,
+   // "m_strvec" uses pmr::get_default_resource().
+   ShoppingList(const ShoppingList& other)
+      : m_strvec(other.m_strvec) {}
+
+   // Copy construct using the given memory_resource.
+   ShoppingList(const ShoppingList& other, allocator_type a)
+      : m_strvec(other.m_strvec, a) {}
+
+   allocator_type get_allocator() const
+   { return m_strvec.get_allocator().resource(); }
+
+   void add_item(const char *item)
+   { m_strvec.emplace_back(item); }
+
+   //...
+};
+
+//]]
+
+//[doc_pmr_main_cpp
+
+//=#include "ShoppingList.hpp"
+#include <cassert>
+#include <boost/container/pmr/list.hpp>
+#include <boost/container/pmr/monotonic_buffer_resource.hpp>
+
+void processShoppingList(const ShoppingList&)
+{  /**/   }
+
+int main()
+{
+   using namespace boost::container;
+   //All memory needed by folder and its contained objects will
+   //be allocated from the default memory resource (usually new/delete) 
+   pmr::list_of<ShoppingList>::type folder; // Default allocator resource
+   //Alternatively in compilers that support template aliases:
+   //    boost::container::pmr::list<ShoppingList> folder;
+   {
+      char buffer[1024];
+      pmr::monotonic_buffer_resource buf_rsrc(&buffer, 1024);
+
+      //All memory needed by temporaryShoppingList will be allocated
+      //from the local buffer (speeds up "processShoppingList")
+      ShoppingList temporaryShoppingList(&buf_rsrc);
+      assert(&buf_rsrc == temporaryShoppingList.get_allocator());
+
+      //list nodes, and strings "salt" and "pepper" will be allocated
+      //in the stack thanks to "monotonic_buffer_resource".
+      temporaryShoppingList.add_item("salt");
+      temporaryShoppingList.add_item("pepper");
+      //...
+
+      //All modifications and additions to "temporaryShoppingList"
+      //will use memory from "buffer" until it's exhausted.
+      processShoppingList(temporaryShoppingList);
+
+      //Processing done, now insert it in "folder",
+      //which uses the default memory resource
+      folder.push_back(temporaryShoppingList);
+      assert(pmr::get_default_resource() == folder.back().get_allocator());
+      //temporaryShoppingList, buf_rsrc, and buffer go out of scope
+   }␍   return 0;
+}
+
+//]