Create a local tsl-robin-mapTargets.cmake to fix issue #45

With this local Targets file the CMake binary directory can be passed to find_package without needing an installation.

Example:
find_package(tsl-robin-map PATHS "/home/user/robin-map/build")
if (tsl-robin-map_FOUND)
    target_link_libraries(my_project PRIVATE tsl::robin_map)
endif()

CMakeLists.txt

@@ -52,8 +52,10 @@ if(${CMAKE_VERSION} VERSION_GREATER "3.2")
             DESTINATION "${CMAKE_INSTALL_DATAROOTDIR}/cmake/tsl-robin-map")
 
 
+    ## Create local tsl-robin-mapTargets.cmake
+    export(TARGETS robin_map NAMESPACE tsl:: FILE "${CMAKE_CURRENT_BINARY_DIR}/tsl-robin-mapTargets.cmake")
 
-    ## Create and install tsl-robin-mapTargets.cmake
+    ## Create and install global tsl-robin-mapTargets.cmake
     install(TARGETS robin_map
             EXPORT tsl-robin-mapTargets)