Support for default block parameters.

[davidahmed]

event_filter = c.eth_newFilter(from_block=str(fromBlock), to_block="latest", address=address, topics=topics)

Would create a filter without raising any error.

But executing logs = c.eth_getLogs(event_filter) raises "BadResponseError: {'jsonrpc': '2.0', 'id': 1, 'error': {'code': -32602, 'message': 'invalid argument 0: json: cannot unmarshal string into Go value of type filters.input'}}"

getFilterChanges and getFilterLogs seem to run fine.