Issue 790: initial commit

Created codes() method. Please review it.
@yegor256 so you suggest to use 

github.randomRepo() there which returns Repo, while I need MkRepo object on which I need to call create() method like below:

.create(
            Json.createObjectBuilder().add("name", "TestCode").build()
);

As interface Repo does not have create() method I use 

github.repos().

there.