Counts the citations in an aux-file.

    @return: defaultdict(int) - {citation_name: number, ...}

def _count_citations(aux_file):
    '''
    Counts the citations in an aux-file.

    @return: defaultdict(int) - {citation_name: number, ...}
    '''
    counter = defaultdict(int)
    with open(aux_file) as fobj:
        content = fobj.read()

    for match in CITE_PATTERN.finditer(content):
        name = match.groups()[0]
        counter[name] += 1

    return counter