Make sure the dict of parsed parameters is in the same order as in the usage text

For example, if you define the following parameters:

```
<param1> <param2>
```

And you parse the parameters:

```
arguments = docopt(__doc__)
```

Then the arguments should be in the same order:

```
print arguments.keys()

-> [param1, param2]
```

This solution uses OrderedDict which is supported in Python 2.7 and higher. It also works with the ordereddict package for Python 2.4-2.6 (https://pypi.python.org/pypi/ordereddict/1.1).