title: Specify compression type in Confluent Python Avro Producer
body: <p>Is there a way to specify the <code>compression.type</code> in producer configs while using the AvroProducer in Confluent's Kafka (python)?</p>
  
  <p>I tried the following:</p>
  
  <pre><code>from confluent_kafka import avro
  from confluent_kafka.avro import AvroProducer
  
  from myconfigs import BOOTSTRAP_SERVER, SCHEMA_REGISTRY_URL, KEY_SCHEMA, VALUE_SCHEMA
  
  avroProducer = AvroProducer({'bootstrap.servers': BOOTSTRAP_SERVER, 'schema.registry.url': SCHEMA_REGISTRY_URL, 'compression.type': 'gzip'},
                              default_key_schema=KEY_SCHEMA, default_value_schema=VALUE_SCHEMA)
  </code></pre>
  
  <p>Got the following error when running this:</p>
  
  <pre><code>Traceback (most recent call last):
    File "confluent_click.py", line 47, in &lt;module&gt;
  default_key_schema=KEY_SCHEMA, default_value_schema=VALUE_SCHEMA)
    File "/usr/local/lib/python3.6/site-packages/confluent_kafka/avro/__init__.py", line 38, in __init__
      super(AvroProducer, self).__init__(config)
  cimpl.KafkaException: KafkaError{code=_INVALID_ARG,val=-186,str="No such configuration property: "compression.type""}
  </code></pre>
  
  <p>Also tried specifying <code>compression_type = 'gzip'</code> as a param to <code>AvroProducer()</code> as</p>
  
  <pre><code>avroProducer = AvroProducer({'bootstrap.servers': BOOTSTRAP_SERVER, 'schema.registry.url': SCHEMA_REGISTRY_URL},
                              default_key_schema=KEY_SCHEMA, default_value_schema=VALUE_SCHEMA, compression_type='gzip')
  </code></pre>
  
  <p>I didn't expect this to succeed and it didn't.</p>
  
  <pre><code>Traceback (most recent call last):
    File "confluent_click.py", line 47, in &lt;module&gt;
      default_key_schema=KEY_SCHEMA, default_value_schema=VALUE_SCHEMA, compression_type='gzip')
  TypeError: __init__() got an unexpected keyword argument 'compression_type'
  </code></pre>
  
  <p>How can I specify <code>compression.type</code> in the producer? I have not been able to find <code>AvroProducer</code>'s documentation.</p>