fix some trivial bugs.
remove online play
reformat code
use with statement to manage file objects.
simplify code and remove download.
remove parameter 'savecookie' of method '__request'. All invocations are passing 'True'.
save qq number and password hash in separated file.
add method delete_task
add method add_task
add method "get_download_info" and "get_aria2c_cmd_line"
introduce url constants.
add method "list_tasks", it returns a list of "TaskInfo"
Download all completed files to current dir and delete them.