Added functionality for fetching pipelines and deals for pipelines

[shanness]

Thanks for the easy to work with library!

This commit adds get_pipelines and get_pipeline_deals
My motivation for this is so I can close rotten deals.

deals = client.get_pipeline_deals(2)
for deal in deals["data"]:
    if (deal["rotten_time"] and deal["status"] == "open"):
        print(deal["rotten_time"],deal["status"])

[yagss]

Hi there, glad to me that you use and contribute in this library, regards