* Add aria2 user and group.
* Use procd to start service.
* Add more supported options.

Compatible with previous version.

Signed-off-by: Hsing-Wang Liao <kuoruan@gmail.com>

* Fix aria2c failed to start after change daemon user, issue #2985;
* Change default download dir;
* Clear exist log file when aria2 start;
* Add log level option;
* Change dir owner when start.

Signed-off-by: Hsing-Wang Liao <kuoruan@gmail.com>

* Add config file.
* Add init.d file.

Signed-off-by: Hsing-Wang Liao <kuoruan@gmail.com>