Support building in Dockerfile dir

[anthony-o]

with --build-in-dockerfile-dir or with

"images": {
  "me/mydockerapp": {"path": "./mydockerapp", "build-in": "dockerfile-dir"}

The other switch exists : --build-in-current-dir

[stephenmelrose]

Not sure why I didn't think of this before! Good addition. As stated in #48, will give this a once over in a week or 2, unless @makeusabrew gets there first.

[makeusabrew]

Cool, no problem with this. Only issue is it's coupled with #48 which I'd like to review a bit first. I'll get this merged locally and make a couple of tweaks, hopefully this evening.

[makeusabrew]

@anthony-o,

I'm really sorry for never merging this; I remember at the time I couldn't merge because it pulled in #48's changes which I wasn't sure about. I tried to cherry pick the relevant commits in today but I've let it diverge so much it proved impossible - really wanted to get your name in the commit log. In the end I implemented this slightly differently but please accept my thanks for the initial prompt to get it in there. Much obliged :)

[anthony-o]

No problem ! Since that time, I built my own project which integrates this thought: https://github.com/iorga-group/docker-cmd ;)