Improved the way specifying a debug deployment works. Added help for the setup task.

Aside from improving the way specifying ``debug`` works. Now more consistent in both use and in code:

```
fab -H ... setup:debug=yes
```

or

```
fab -H ... setup:debug=no
```

Default is **no**

This also adds help for the ``setup`` task:

```
$ fab help:setup
Help on setup:

Setup a full prodction deployment

    Options:

        tag   - "latest" or "dev" or any valid git tag.
        debug - Whether or not to deploy a debug deployment (Default: no)

```