Introducing docker build action.

* can be helpful with asynchronous creating docker containers from Dockerfile.
* can accept both local path and remote url.
* it's completely asynchronous, based on tornado http client.
* no unix socket yet, but it's possible.
Framework now can use asynchronous HTTP over unix domain sockets.

* it's useful to communicate with docker.
Docker info implemented.

* asynchronous, of course
* some functional decomposition done.
Introducing docker images command.

* asynchronous and yieldable
Passing additional options to the docker.

* also more convenient naming.
Docker push asynchronous API is ready.

* refactoring over docker.Client
* default timeout is now global constant
Now docker module can retrieve container list.