get_next_available

See merge request asapo/asapo!204

Allow sending objects supporting the buffer interface

Closes #7

See merge request asapo/asapo!187

Add optional argument `ordered` to consumer function get_next. If true messages will be ordered by message_id otherwise by _id.

Add boolean parameter `ordered` to request get_next. If True, it returns next by message_id, if not by _id.

Speedup get_next

See merge request asapo/asapo!203

This includes read-only buffers.

The code split between bytes and numpy array is removed and all objects
are now handled equally.

Furthermore, it seems to be more correct to increase the ref count for
None objects as well, while a pointer to that object is used.

Enable test of receiver with kafka. Add sleep of 3 sec after start of kafka listener to ensure that is it ready