add script that runs a cpu benchmark of downloading

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8930 a83610d8-ad2a-0410-a6ab-fc0612d85776
extend benchmark to run both upload and download tests

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8931 a83610d8-ad2a-0410-a6ab-fc0612d85776
fix backwards compatibility with tracker_url and async_add_torrent

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8933 a83610d8-ad2a-0410-a6ab-fc0612d85776