volume support enhancements

this is meant to replace #60. in addition to resolving issue #55, it also addresses #62 to allow container volumes to be specified at image build time. (i split off the assembly enhancements into #64).

all options are supported in the property files, there are some new tests, and some compiler warning cleanup.

i have also update the docs and did some minor re-organization which i hope you won't mind (i think having `docker:build` come before `docker:start` makes sense from a workflow perspective and i think listing config values in alphabetical order makes scanning the docs for what you need easier).
Are you sure that the volume to be specified within "Volumes" in the create configuration should be the host path ? I'm not sure, but I think it should be the container path (element [1]). The documentation is not really clear about this. The best I could find was docker/docker#1580.