Issue6: rename 'ports' into 'expose' and use 'ports' to publish

[simonbahuchet]

Hello David,

The keyword 'ports' is currently used in the yaml configuration file to expose some ports (to be able to link other containers) If I am not mistaken, it corresponds to the "expose" keyword in docker and fig.

I propose the follwoing changes:

• keyword 'ports' is renamed into 'expose'
• a new 'ports' is added to publish the ports to the host
• the documentation is updated accordingly
• an example is added to test with a simple elasticsearch cluster

[labisso]

Thanks Simon! These changes look great.