mkdir for MegaFS

##### megaclient.py
    def createdir(self, target, dirname):
        key =  [random.randint(0, 0xFFFFFFFF) for _ in xrange(4)]
        attributes = {'n': dirname}
        enc_attributes = enc_attr(attributes, key)
        return self.api_req({'a': 'p', 't': target, 'n': [{'h': 'xxxxxxxx', 't': 1, 'a': base64urlencode(enc_attributes), 'k': a32_to_base64(encrypt_key(key, self.master_key))}]})
##### megaclient.py


##### megafs.py
    def mkdir (self, path, mode):
        dirname, basename = os.path.split(path)
        created_folder = self.client.createdir(self.files[dirname]['h'], basename)
        if 'f' in created_folder:
            created_folder = self.client.processfile(created_folder['f'][0])
            self.files[dirname]['children'].append(basename)
            self.files[path] = created_folder
            self.files[path]['children'] = []
##### megafs.py