2.0.12.4

• crash: don't crash if a null set_piece_hashes_listener is passed to set_piece_hashes_ex
• libraries are now compiled with C++20 (ming/windows with C++2a which is the same)
• g++-9 upgraded to g++-11 for linux build
• new Sha256Hash::swig()
• new SessionManager::find(Sha256Hash) and SessionManager::find(TorrentInfo) methods
• built with android NDK r28c with 16K page size support
• Android 64-bit binaries are compiled to have 16KB max-page-size