Added contextual service runner + tests
updated docstring from out of date usage
updated contextual runner to provide neater api.
updated tests to demonstrate usage
Merge branch 'master' of github.com:onefinestay/nameko into runner-context-manager

Conflicts:
	test/test_service_runner.py
Neater implementation of contextual service runner with updated tests
Merge branch 'master' of github.com:onefinestay/nameko into runner-context-manager

Conflicts:
	nameko/runners.py
	test/test_service_runner.py
line length
renaming context manager
whitespace
stray
use sets instead of lists for neater comparison
Merge pull request #94 from onefinestay/runner-context-manager

Contextual service runner