Small usability improvements

Common shorthands and deprecation warnings.

```
myhost% ./cjdroute -v
Cjdns Git Version ID: 79c2bb7667ca395e1a6997563b67c16cbfcf6183
myhost% ./cjdroute -h
Usage: ./cjdroute [--help] [--genconf] [--bench] [--version] [--cleanconf]

To get the router up and running.
Step 1:
  Generate a new configuration file.
    ./cjdroute --genconf > cjdroute.conf

Step 2:
  Find somebody to connect to.
  Check out the IRC channel or http://hyperboria.net/
  for information about how to meet new people and make connect to them.

Step 3:
  Fire it up!
    sudo ./cjdroute < cjdroute.conf

For more information about other functions and non-standard setups, see README.md
myhost% ./cjdroute --pidfile
'--pidfile' option is deprecated.
myhost% ./cjdroute --pidfile 202002.pid
./cjdroute: too many arguments
Try `./cjdroute --help' for more information.

'--pidfile' option is deprecated.
```