Write some data to the handle at the specified offset.
template< typename ConstBufferSequence> std::size_t write_some_at( boost::uint64_t offset, const ConstBufferSequence & buffers); template< typename ConstBufferSequence> std::size_t write_some_at( boost::uint64_t offset, const ConstBufferSequence & buffers, asio::error_code & ec);