tproxy support for script cli args

extend tproxy such that command line arguments can be passed all the way to the called script.

Current workaround:

assume the following command line (notice the extra --remote argument):

``` bash
$ dproxy.py --daemon --log-file=MyLogFile.log --bind=127.0.0.1:5678 --remote=130.130.130.130:6789 transparent2.py
```

where dproxy.py replaces tproxy by supporting the --remote cli argument as follows:

``` python
from tproxy.app import run
from tproxy.config import *
import os

class RemoteAddress(Setting):
name = "remote"
section = "the address of the remote host"
cli = ["-r", "--remote"]
meta = "REMOTEADDRESS"
default = "127.0.0.1:8080"
validator = validate_string
desc = """\
address of remote host to connect to
"""
run()
```

while transparent2.py would look as follows:

``` python
import argparse

# parse the arguments
parser = argparse.ArgumentParser()
parser.add_argument('--remote', dest='remote', action='store', type=str, default=None)
args, remainder = parser.parse_known_args()

ip, port = args.remote.split(':')

def proxy(data):
return {'remote': (ip, int(port))}
```

although this approach works, it's still nicer if tproxy would provide support for extra cli arguments and possibly facilitate access to them without going through argparse in the called script.