Fix function error.
Fix path problem.

make aria2addbt.py can called in other dir.
Fix options proble.
Add aria2 wrapper.
Add eval function to excute unknown command.
Implement list single download by gid.
Use rpc secret in config if not not specified.
Add comment.
Add execute function.

more convinence if call by other program.
Add option operation.
Implement pause function.
Implement remove function.
Implement clear function.
Implement save function.
Auto require status key in list().
list() accept 3 new keys.

errer, removed, completed are all return by tellStopped(), now can be used.
list() now accept 'queueing' key.
Update document.
Fix: number of status should return correctly.

Affect: waiting, paused, error, removed, completed keys
Now offset and num also affect key 'active'.