API for supported parameters

This adds a daemon API for supported parameters, as they correlate to
text arguments to client commands. This way the client can display
accurate options even if it is a different version than the daemon. Or
interaction with only the API could access parameter information.

fixes https://github.com/docker/docker/issues/6889


For example, in the following, the usage of `--filter` includes parameters enumerated from the server.
```
vbatts@noyee ~ (master) $ /home/vbatts/src/docker/docker/bundles/1.1.2-dev/dynbinary/docker-1.1.2-dev images -h

Usage: docker images [OPTIONS] [NAME]

List images

  -a, --all=false      Show all images (by default filter out the intermediate image layers)
  -f, --filter=[]      Provide filter values. Filters include:
                         - dangling = <true|false>
                           shows only images with no name
                           (would show in the list as <none>)
  --no-trunc=false     Don't truncate output
  -q, --quiet=false    Only show numeric IDs
vbatts@noyee ~ (master) $ /home/vbatts/src/docker/docker/bundles/1.1.2-dev/dynbinary/docker-1.1.2-dev ps -h

Usage: docker ps [OPTIONS]

List containers

  -a, --all=false       Show all containers. Only running containers are shown by default.
  --before=""           Show only container created before Id or Name, include non-running ones.
  -f, --filter=[]       Provide filter values. Filters include:
                          - exited = <int>
                            containers with exit code of <int>
  -l, --latest=false    Show only the latest created container, include non-running ones.
  -n=-1                 Show n last created containers, include non-running ones.
  --no-trunc=false      Don't truncate output
  -q, --quiet=false     Only display numeric IDs
  -s, --size=false      Display sizes
  --since=""            Show only containers created since Id or Name, include non-running ones.

```