Add support for modular build structure. (#79)

* Make the library modular usable.

* Switch to library requirements instead of source. As source puts extra source in install targets.

* Add requires-b2 check to top-level build file.

* Bump B2 require to 5.2

* Change all <source> references to <library>.

* Update copyright dates.

* Move inter-lib dependencies to a project variable and into the build targets.

* Update build deps.

Jamfile

@@ -1,11 +0,0 @@
-#  Boost.MPL Library Jamfile
-#
-#  Copyright (c) 2018 James E. King III
-#
-#  Use, modification, and distribution are subject to 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)
-
-# please order by name to ease maintenance
-build-project example ;
-build-project test ;

build.jam

@@ -0,0 +1,29 @@
+# Copyright René Ferdinand Rivera Morell 2023-2024
+# 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)
+
+require-b2 5.2 ;
+
+constant boost_dependencies :
+    /boost/config//boost_config
+    /boost/core//boost_core
+    /boost/predef//boost_predef
+    /boost/preprocessor//boost_preprocessor
+    /boost/static_assert//boost_static_assert
+    /boost/type_traits//boost_type_traits
+    /boost/utility//boost_utility ;
+
+project /boost/mpl
+    : common-requirements
+        <include>include
+    ;
+
+explicit
+    [ alias boost_mpl : : : : <library>$(boost_dependencies) ]
+    [ alias all : boost_mpl example test ]
+    ;
+
+call-if : boost-library mpl
+    ;
+

example/Jamfile.v2

@@ -7,9 +7,11 @@
 
 import testing ;
 
+project : requirements <library>/boost/mpl//boost_mpl ;
+
 test-suite "mpl-examples"
    :    [ run     inherit_linearly.cpp ]
         [ compile integer.cpp ]
-        [ run     tuple_from_list.cpp ]
+        [ run     tuple_from_list.cpp : : : <library>/boost/tuple//boost_tuple ]
    ;
 

test/Jamfile.v2

@@ -1,5 +1,6 @@
 project
     :   requirements
+        <library>/boost/mpl//boost_mpl
         <warnings>extra
         <toolset>clang:<cxxflags>-Wno-variadic-macros
         <toolset>gcc:<cxxflags>-Wshadow
@@ -49,7 +50,8 @@ compile find.cpp ;
 compile find_if.cpp ;
 compile fold.cpp ;
 run for_each.cpp
-  : : : <cxxstd>98:<build>no <cxxstd>03:<build>no ;
+  : : : <cxxstd>98:<build>no <cxxstd>03:<build>no
+    <library>/boost/bind//boost_bind ;
 compile front.cpp ;
 compile get_tag_def.cpp ;
 compile has_xxx.cpp ;