Fixed auto-generated documentation in grunt --help.

Requires #133.

#### Before
```sh
$ grunt --help
Available tasks
...
           install  Alias for "mozilla-addon-sdk" task.
           default  Alias for "clean", "less", "css2js", "jshint", "concat",
                    "copy", "sed" tasks.
              test  Alias for "qunit" task.
         travis-ci  Alias for "default", "test" tasks.
       autoload:ff  Autoload new XPI extension in Firefox
      build:chrome  Alias for "compress:chrome" task.
     build:firefox  Alias for "mozilla-cfx-xpi" task.
      build:safari  Builds the safari extension
             build  Alias for "default", "compress:chrome", "build:firefox",
                    "build:safari" tasks.
```
#### After
```sh
$ grunt --help
Available tasks
...
           install  Installs dependencies.
           default  Compiles code.
            dev:ff  Compiles code to build a Firefox extension. (see watch:ff)
          watch:ff  Enables real-time development for Firefox.
              test  Runs tests.
         travis-ci  Compiles code and runs tests.
             build  Compiles code and builds all extensions.
      build:chrome  Builds the Chrome extension.
     build:firefox  Builds the Firefox extension.
      build:safari  Builds the Safari extension.
       autoload:ff  Loads the XPI extension into Firefox.
```