[feat] Support consumer batch receive.

[shibd]

Motivation

#39

Modifications

• Support consumer batch receive.

[BewareMyPower]

Could you wrap the BatchReceivePolicy class into the pulsar module? It's better to avoid using the class from _pulsar module directly.

[shibd]

Could you wrap the BatchReceivePolicy class into the pulsar module? It's better to avoid using the class from _pulsar module directly.

Yes, When I coded, I struggled with whether to implement a wrapper. It turns out that implementing a wrapper class can clearly define the input parameters and docs.

I changed it, PTAL.

[tisonkun]

@shibd you may try to rebase on the latest master so that we're sure there's no doc string syntax regression :)