fix #12: deprecate NewCompletionCommand

optimize graceful package and bump go.octolab.org

rethink graceful package

fix #11: add graceful.Shutdown to handle exit process

refactor Silent error

fix #9: add Silent error

simplify completion and version commands

fix #8: define autocompletion format based on SHELL environment variable

update license and remove dev environment

Merge pull request #6 from octolab/issue-5

fix issue #5