updating changelog for 0.4.5 release
updating changelog for 0.4.5 release

sferik/yajl-ruby,brianmario/yajl-ruby,mrkn/yajl-ruby,tenderlove/yajl-ruby,brianmario/yajl-ruby,tenderlove/yajl-ruby,brianmario/yajl-ruby,sferik/yajl-ruby,sferik/yajl-ruby