Merge pull request #17 from nikicat/master

package paths refactored, yandex-specifics removed, bug fixes
actions: updated help message
printdiff: wider diff lines
new: SourceImage added
entities.Image: repository field splitted to registry+repository
style fixes
entities.Image: use DockerException for errors in response stream
entities.SourceImage: add newlines at end of ENV and RUN stanzas