New flags

First step toward getopt style flags:

As we keep compatibility with flags like `-dns` we can't have `-i -t -> -it`
but at least `-` and `--` are now correct

- [x] code
- [x] documentation
- [x] auto complete scripts

All previously flags are still compatible, **no functional change**, but new flag introduced:

Previously:
```
Usage of /home/vagrant/docker:
  -D=false: Enable debug mode
  -H=[]: Multiple tcp://host:port or unix://path/to/socket to bind in daemon mode, single connection otherwise
  -api-enable-cors=false: Enable CORS headers in the remote API
  -b="": Attach containers to a pre-existing network bridge; use 'none' to disable container networking
  -d=false: Enable daemon mode
  -dns=[]: Force docker to use specific DNS servers
  -g="/var/lib/docker": Path to use as the root of the docker runtime
  -icc=true: Enable inter-container communication
  -ip="0.0.0.0": Default IP address to use when binding container ports
  -iptables=true: Disable docker's addition of iptables rules
  -p="/var/run/docker.pid": Path to use for daemon PID file
  -r=true: Restart previously running containers
  -s="": Force the docker runtime to use a specific storage driver
  -v=false: Print version information and quit
```

Now:
```
Usage of docker:
  -D, --debug=false: Enable debug mode
  -H, --host=[]: Multiple tcp://host:port or unix://path/to/socket to bind in daemon mode, single connection otherwise
  --api-enable-cors=false: Enable CORS headers in the remote API
  -b, --bridge="": Attach containers to a pre-existing network bridge; use 'none' to disable container networking
  --bip="": Use this CIDR notation address for the network bridge's IP, not compatible with -b
  -d, --daemon=false: Enable daemon mode
  --dns=[]: Force docker to use specific DNS servers
  -g, --graph="/var/lib/docker": Path to use as the root of the docker runtime
  --icc=true: Enable inter-container communication
  --ip="0.0.0.0": Default IP address to use when binding container ports
  --iptables=true: Disable docker's addition of iptables rules
  -p, --pidfile="/var/run/docker.pid": Path to use for daemon PID file
  -r, --restart=true: Restart previously running containers
  -s, --storage-driver="": Force the docker runtime to use a specific storage driver
  -v, --version=false: Print version information and quit
```