* added constexpr/compile-time hash computation to const_string (based on 32-bit murmurhash3)
 * make use of precompiled headers in xcode (prefix.pch); this however requires disabling extern templates (separate template instantiation)
 * removed unnecessary destructors from constexpr classes again (now that the clang bug is fixed)
 * removed obsolete template helper functions from core/util.hpp
 * copyright info update to 2014