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).