Fix #267 'SQLiteCpp/SQLiteCpp.h' file not found

Issue introduced by Commit a166062 Significantly improved support for external sqlite3, and generalized thread and dl libs on Unix/Linux/Mac

Author: SRombauts

CMakeLists.txt

@@ -252,6 +252,9 @@ install(TARGETS SQLiteCpp
     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
     ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
     COMPONENT libraries)
+target_include_directories(SQLiteCpp PUBLIC
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  $<INSTALL_INTERFACE:include/>)
 install(DIRECTORY include/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR} COMPONENT headers FILES_MATCHING REGEX ".*\\.(hpp|h)$")
 install(EXPORT ${PROJECT_NAME}Targets DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME})