fix yaml parsing:  multiple tags must be space-separated, not comma-separated

was ignoring the tag to inform Unmarshall the name of the field for yml
allow the dockerfile specification to use environment vars
Merge pull request #11 from rliebling/fix_yaml_parsing

Fix YAML parsing: multiple tags must be separated by space, not comma
Merge pull request #12 from rliebling/allow_env_vars_for_dockerfile

allow the dockerfile specification to use environment vars
Bump version to 0.6.1
Move print functions into their own package
Move command handling into cmd.go
Use long option names

Short names such as `-rm` are deprecated as of Docker 0.9.
add option to specify config file

allows one to have multiple configuration files (json/yml) in same dir
and select which to use via cmdline option