add command arguments to use conf parser, and stdout output plugin

Command arguments and stdout plugin are added.

Currently '-c' and '-h' are implemented, so ik can be executed like these.
```
go run main.go -c ./test.conf
go run main.go -h
```

test.conf is as follows.
```
<source>
  type forward
  port 24224
</source>

<match **>
  type stdout
</match>
```