addcontext: fixed context restore on exit
some RuntimeErrors replaced with asserts
SourceImage: refactored CMD and ENTRYPOINT commands support
Container: calculate "hostname" when starting container
support "closure-files" for ConfigVolume
removed resource file loading support from TextFile
Ship.spawn: added "sudo" option
fixed Ship.upload
Ship: added more logs for ssh commands
LocalShip: added black "restart" method
improved __repr__ format for Container and Door
Door: support empty formatspec in __format__
Container.fullname should work even without ship
Volume.erase should use sudo for erasing
added "container enter" subcommand
added custom argument support for "shipment generate"
use nondefault flow style for "shipment generate" output
added IniFile
added docstring to make_backrefs
refactored Door/Url entities