Merge pull request #25 from bjaglin/fixdoc

fix inline example
document the different effects of the -f/--force flag
clarify use of -g/--group
fix copy/paste
clarify "build or else pull" behavior
reflect possibility of restricting the affected containers via -g
commands currently don't take arguments, so fail if there is any
typo and unecessary comma
Merge pull request #29 from bjaglin/typo

typo and unecessary comma
Merge pull request #28 from bjaglin/arguments

Fail the command if a parameter is not used
support status code hint in panic()
propagate `docker` status code on error
CONFIGURATION_ERROR for missing configuration
IO_ERR for issues when opening config file
DATA_ERR when config unmarshalling fails
USAGE for invalid CLI input detected by cobra
USAGE for unused arguments
USAGE for invalid group/container reference
Merge pull request #30 from bjaglin/statuscodes

Map runtime errors to process status codes so that crane can be used within scripts
Bump version to 0.7.1