lx download name:xxx (same as lx download raw:xxx)
refactor page_size
lx list --limit=NUM
refactor read_all_tasks
fetch pages on demand
automatically set limit
fix limit in OnDemandTaskList (but still buggy code)
remove login check for better performance
lx list --page-size=10
fix auto-login
Add IDM as a download tool.
Completely remove file check with "no hash" option on.