support for depends_on

• depends on now is shown as a link in the link graph

support volumes

• consider volumes as system boundaries
• links services to these volumes

legacy docker-compose support

• added support for legacy docker-compose format

renders system boundaries

• renders system boundaries. currently it uses exposed ports with its aliases.

ignore alias names for links

• ignores alias names for links

initial release

allows generating link graphs for docker-compose files.
just supports docker-compose version 2.