Rtbkit 634 http bidding interface example

Adds python implementation of a bid agent using http api.
Actually as can be seen at the wiki page I've written about this example, the config JSON sent to Configuration agent has a list of creatives the agent will bid on. Take a look at: https://github.com/rtbkit/rtbkit/wiki/How-to-write-a-bidding-agent-using-Python-and-HTTP-API#agent-configuration

And the variable self.bid_config["creatives"] = data["creatives"] actually read from that same json the array of creatives.

That said, in the example I am only using the first one, because my config file had only one creative. So I guess I should add this as a comment.