Install headers prefixed, as to not cause a possible conflict with
different versions.

--- templates/lib/CMakeLists.txt.orig	2016-08-10 16:09:48 UTC
+++ templates/lib/CMakeLists.txt
@@ -137,7 +137,7 @@ install(TARGETS Grantlee_Templates EXPOR
          RUNTIME DESTINATION ${BIN_INSTALL_DIR} COMPONENT Templates
          LIBRARY DESTINATION ${LIB_INSTALL_DIR} COMPONENT Templates
          ARCHIVE DESTINATION ${LIB_INSTALL_DIR} COMPONENT Templates
-         INCLUDES DESTINATION include
+         INCLUDES DESTINATION include/grantlee5
 )

 install(FILES
