Allow writing to S3 paths
It would be really great if `to_(filetype)` supported writing to S3. 

Here is an example upload to s3 function that takes in a local file and places it on a s3 bucket.

``` python
def upload_to_s3(local_file_path, file_name, bucket_name, s3_directory):
    """
    Returns
    ----------
    Uploads local file to appropriate s3 key, and prints status 

    Parameters
    ----------
    local_file_path : str
        ex. 'my/local/path'
    file_name : str
        ex. 'cleaned_data.csv'
    bucket_name : str
        ex. 'dsapp-edu-data'
    s3_directory : str
        ex. 'NC-Cabarrus/cleaned_data'
    """

    def percent_cb(complete, total):
        """
        Helper function that prints progress
        """
        sys.stdout.write('.')
        sys.stdout.flush()

    conn = boto.connect_s3()
    bucket = conn.get_bucket(bucket_name)
    full_key_name = os.path.join(s3_directory, file_name)
    k = bucket.new_key(full_key_name)
    full_filepath = os.path.join(local_file_path, file_name)
    k.set_contents_from_filename(full_filepath, cb=percent_cb, num_cb=10)

    return None 
```
