Add support for \n in usages

Change (slightly) the way usages are displayed (inspired from `ls`) & and add `host` for `--net`

Take a look at `--net`

Before:
```
Usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

Run a command in a new container

  -a, --attach=[]: Attach to stdin, stdout or stderr.
  -c, --cpu-shares=0: CPU shares (relative weight)
  --cidfile="": Write the container ID to the file
  -d, --detach=false: Detached mode: Run container in the background, print new container id
  --dns=[]: Set custom dns servers
  --dns-search=[]: Set custom dns search domains
  -e, --env=[]: Set environment variables
  --entrypoint="": Overwrite the default entrypoint of the image
  --env-file=[]: Read in a line delimited file of ENV variables
  --expose=[]: Expose a port from the container without publishing it to your host
  -h, --hostname="": Container host name
  -i, --interactive=false: Keep stdin open even if not attached
  --link=[]: Add link to another container (name:alias)
  --lxc-conf=[]: (lxc exec-driver only) Add custom lxc options --lxc-conf="lxc.cgroup.cpuset.cpus = 0,1"
  -m, --memory="": Memory limit (format: <number><optional unit>, where unit = b, k, m or g)
  --name="": Assign a name to the container
  --net="bridge": Set the Network mode for the container ('bridge': creates a new network stack for the container on the docker bridge, 'none': no networking for this container, 'container:<name|id>': reuses another container network stack)
  -p, --publish=[]: Publish a container's port to the host (format: ip:hostPort:containerPort | ip::containerPort | hostPort:containerPort) (use 'docker port' to see the actual mapping)
  -P, --publish-all=false: Publish all exposed ports to the host interfaces
  --privileged=false: Give extended privileges to this container
  --rm=false: Automatically remove the container when it exits (incompatible with -d)
  --sig-proxy=true: Proxify all received signal to the process (even in non-tty mode)
  -t, --tty=false: Allocate a pseudo-tty
  -u, --user="": Username or UID
  -v, --volume=[]: Bind mount a volume (e.g. from the host: -v /host:/container, from docker: -v /container)
  --volumes-from=[]: Mount volumes from the specified container(s)
  -w, --workdir="": Working directory inside the container
```

Now:
```
Usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

Run a command in a new container

  -a, --attach=[]            Attach to stdin, stdout or stderr.
  -c, --cpu-shares=0         CPU shares (relative weight)
  --cidfile=""               Write the container ID to the file
  -d, --detach=false         Detached mode: Run container in the background, print new container id
  --dns=[]                   Set custom dns servers
  --dns-search=[]            Set custom dns search domains
  -e, --env=[]               Set environment variables
  --entrypoint=""            Overwrite the default entrypoint of the image
  --env-file=[]              Read in a line delimited file of ENV variables
  --expose=[]                Expose a port from the container without publishing it to your host
  -h, --hostname=""          Container host name
  -i, --interactive=false    Keep stdin open even if not attached
  --link=[]                  Add link to another container (name:alias)
  --lxc-conf=[]              (lxc exec-driver only) Add custom lxc options --lxc-conf="lxc.cgroup.cpuset.cpus = 0,1"
  -m, --memory=""            Memory limit (format: <number><optional unit>, where unit = b, k, m or g)
  --name=""                  Assign a name to the container
  --net="bridge"             Set the Network mode for the container
                               'bridge': creates a new network stack for the container on the docker bridge
                               'none': no networking for this container
                               'container:<name|id>': reuses another container network stack
                               'host': use the host network stack
  -P, --publish-all=false    Publish all exposed ports to the host interfaces
  -p, --publish=[]           Publish a container's port to the host
                               format: ip:hostPort:containerPort | ip::containerPort | hostPort:containerPort
                               (use 'docker port' to see the actual mapping)
  --privileged=false         Give extended privileges to this container
  --rm=false                 Automatically remove the container when it exits (incompatible with -d)
  --sig-proxy=true           Proxify all received signal to the process (even in non-tty mode)
  -t, --tty=false            Allocate a pseudo-tty
  -u, --user=""              Username or UID
  -v, --volume=[]            Bind mount a volume (e.g. from the host: -v /host:/container, from docker: -v /container)
  --volumes-from=[]          Mount volumes from the specified container(s)
  -w, --workdir=""           Working directory inside the container
```

ping @crosbymichael