Remove hard error about C++11 requirement and update CI

test/Jamfile.v2

@@ -12,7 +12,7 @@ import ../../config/checks/config : requires ;
 
 project
     : requirements
-        [ requires cxx11 ]
+        [ requires cxx11_rvalue_references ]
         # default to all warnings on:
         <warnings>all
         # set warnings as errors for those compilers we know we get warning free:

test/appveyor.yml

@@ -21,7 +21,7 @@ init:
 # From this point and below code is same for all the Boost libs
 ###############################################################################################################
 
-version: 1.71.{build}-{branch}
+version: 1.84.{build}-{branch}
  
 # branches to build
 branches:
@@ -32,9 +32,6 @@ skip_tags: true
 
 environment:
   matrix:
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-      TOOLSET: msvc-9.0,msvc-10.0,msvc-11.0,msvc-12.0
-      ADDRMD: 32
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
       TOOLSET: msvc-14.1,clang-win
       CXXSTD: 14,17