add GhostOpener, rename contrib/sina to contrib/weibo
remove GhostOpener; add mechanism to incremental crawl
add Url to cola/core/unit, set Url.force to True will not be deduplicated
add SpynnerOpener which support running JS and Ajax; add contrib/weibosearch; issue: now SpynnerOpener may be identified as a robot
fixes on contrib/weibosearch
change MechanizeOpener gzip handle by experimentally add set_handle_zip(True)
fix weibo(including fans and follows) next page url fetch approach