manual: fix compilation errors and warnings
manual: fix compilation errors and warnings

cffi/cffi,attila-lendvai/cffi,dkochmanski/cffi,mcna/cffi,dkochmanski/cffi,3b/cffi,cffi/cffi,stassats/cffi,3b/cffi,dkochmanski/cffi,attila-lendvai/cffi,stassats/cffi,cffi/cffi,3b/cffi,mcna/cffi,stassats/cffi