Merge pull request #52 from nikicat/master

refactoring and new commands
fixed Container.__repr__ exception
compare_volumes should differ if some file doesn't exist
BaseFile: support directories in file name
added "privileged" Container attr
TextFile: "text" and "filename" args swapped (to deprecate "filename" in future)
compare_container: added "user" and "privileged" to comparison
added "container remove" command
Task support refactored, added "task exec" command