add ability to build Apple framework using CMAKE_FRAMEWORK

CMakeLists.txt

@@ -252,6 +252,7 @@ set(FMT_DEBUG_POSTFIX d CACHE STRING "Debug library postfix.")
 
 set_target_properties(fmt PROPERTIES
   VERSION ${FMT_VERSION} SOVERSION ${CPACK_PACKAGE_VERSION_MAJOR}
+  PUBLIC_HEADER "${FMT_HEADERS}"
   DEBUG_POSTFIX "${FMT_DEBUG_POSTFIX}")
 
 # Set FMT_LIB_NAME for pkg-config fmt.pc. We cannot use the OUTPUT_NAME target
@@ -329,6 +330,7 @@ if (FMT_INSTALL)
   install(TARGETS ${INSTALL_TARGETS} EXPORT ${targets_export_name}
           LIBRARY DESTINATION ${FMT_LIB_DIR}
           ARCHIVE DESTINATION ${FMT_LIB_DIR}
+          FRAMEWORK DESTINATION "."
           RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
 
   # Use a namespace because CMake provides better diagnostics for namespaced