CMakeLists: include path fix + compatibility.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c02301c..be860c9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -195,7 +195,7 @@
 # Add an interface target to export it
 add_library(RapidJSON INTERFACE)
 
-target_include_directories(RapidJSON INTERFACE $<INSTALL_INTERFACE:include/rapidjson>)
+target_include_directories(RapidJSON INTERFACE $<INSTALL_INTERFACE:include>)
 
 install(DIRECTORY include/rapidjson
     DESTINATION "${INCLUDE_INSTALL_DIR}"

RapidJSONConfig.cmake.in

diff --git a/RapidJSONConfig.cmake.in b/RapidJSONConfig.cmake.in
index a8ca78f..0ee1d9d 100644
--- a/RapidJSONConfig.cmake.in
+++ b/RapidJSONConfig.cmake.in
@@ -17,3 +17,7 @@
 get_target_property(RapidJSON_INCLUDE_DIR RapidJSON INTERFACE_INCLUDE_DIRECTORIES)
 
 set( RapidJSON_INCLUDE_DIRS ${RapidJSON_INCLUDE_DIR} )
+
+if(NOT TARGET rapidjson)
+  add_library(rapidjson ALIAS RapidJSON)
+endif()