http_client: Add a swagger-py Asynchronous HTTP client
http_client: Add a swagger-py Asynchronous HTTP client

This patch adds the basics for an asynchronous swagger-py compatible HTTP
client. With this client, we can use swagger-py to parse and dynamically
build the resources from an Asterisk server (and not have to do the work
ourselves, or hard code things).

matt-jordan/twisted-ari