'Add completion-type suggestion:
http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-suggesters-completion.html
:param text: text for searching using autocompletion
:param name: name for the suggester
:param field: document\'s field to be autocompleted
:param size: (optional) size of the autocomplete list
:return:'

def add_completion(self, text, name, field, size=None, params=None):

    data = {'field': field}
    if size:
        data['size'] = size
    if params:
        data.update(params)
    self.fields[name] = {'text': text, 'completion': data}
