feat(gci): add a gci.yaml file

[arschles]

This is a proof-of-concept that shows an integration with gci. If you have a GCI binary

A few limitations, and their planned fixes:

• No ability to parameterize docker image repositories, names, tags, etc: Allow docker target images to be specified by env vars arschles/godo#78
• No ability to run go test $(glide nv): Allow custom commands to execute other commands arschles/godo#79
• No target dependencies: Support target dependencies arschles/godo#18
• No ability to build/push docker images: build multiple images arschles/godo#22

This PR should remain open (with no given milestone) until gci has the above features completed

Related tangentially to #194, since gci may be an alternative to captain

[krancour]

Oh wow. This is cool @arschles! My initial reaction to this is that is feels like a better fit than captain for how we tend to work. I am looking forward to digging into this more.