`Chain` object returned from `Service` now initialized with service's event loop.
Convenient event loop name in `gen_test` decorator.
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.
Useless asserts has been removed.
Refactoring over `cocaine.futures.Future` class.

* convenient naming
* states
* guard asserts
* thread safety
Merge pull request #8 from cocaine/refactoring.futures

Refactoring over `cocaine.futures.Future` class.
Code style.
Merge branch 'refactoring.futures'
More meaningful error messages in `Locator.resolve` method.
Fixed Liskov substitution principe in `cocaine.futures.Future` hierarchy.

* `Future.is_bound` method added to check its state.
* `Future.close method` checks its state before actual closing. It's safe to call this method multiple times.
* `cocaine.futures.chain.PreparedFuture` and `cocaine.futures.chain.Deferred` refactored and simplified.
Bug fixed.

* double choking.
Minor style.
Minor style again.
Drop deprecated method.