Add tags for option variables
Update URLs for the latest code and document
Merge branch 'improve-help'

Close gh-4.
Add a Gemfile for development dependencies
Add a Rakefile for routine works
Add a configuration file for Travis CI
Ignore intermediate files for utilities
Farewell to mduem
Merge branch 'migrate-to-vim-flavor'
Add an option to keep a leaving key
Merge branch 'keep-leaving-key'

Close gh-6.
Fix a typo
Fix a list item for readability
Update copyright notices
Bump up version to 0.1.0
Add release notes
Merge branch 'prepare-0.1.0'