Add pouch/client package about pouch

[Ace-Tang]

sure, I will integrate client and cli package

[allencloud]

Yes, I strongly agree what Letty said.

For RESTful API pouchd provides, almost we can divide into two kinds of callers for end-users:

• Command Line to pouchd;
• A program integrating API client to call pouchd;

While more technically, the first part is also to encapsulate API client to make calls torwards pouchd. Therefore, I recommend that we should split the command line codes and API client side code.

I think @Ace-Tang has started the latter parts, while there are still some codes coupling in the code base, such as:
https://github.com/alibaba/pouch/blob/master/cli/pull.go#L35-L50
https://github.com/alibaba/pouch/blob/master/cli/stop.go#L29-L32
https://github.com/alibaba/pouch/blob/master/cli/start.go#L27-L30
and so on.

Would you like to help make code decouple explicitly, and command line codes are responsible for cli, API client code are responsible for api calling? @Ace-Tang
I think this is really important at the very beginning of project pouch. So maybe we should promote the priority of this work.

[allencloud]

That could not be better!!! 🥂

[allencloud]

I think we have already walked on the right direction, thanks to @Ace-Tang 's contribution. Closing this issue.