checks '_docs' and '_posts' directories by default.
change argument style.
save '_docs' and '_posts' directories by default.
accept arguments for revision and target_dir.
update extras.md fix #165
typo in key of base_revision
update plugins.md based e57cd00. fix #175
Translate, to close #186
modify based on comments
Merge pull request #210 from harupong/issue186

Translate, to close #186
Merge pull request #207 from melborne/update-extras.md

update extras.md fix #165
Merge pull request #203 from melborne/check-releases-update

'_post' ディレクトリ追従のためのRakefileの更新
_posts以下のファイルをIssue
update variables.md
fix typo in our CONTRIBUTING.md
rake-togglate now succeeds
update upgrading.md
update troubleshooting.md
Merge pull request #239 from satoso/contrib_typo

fix typo in our CONTRIBUTING.md
Merge pull request #240 from satoso/iss183

update upgrading.md
Merge pull request #241 from satoso/iss182

update troubleshooting.md
Merge pull request #209 from melborne/update-plugins.md

update plugins.md based e57cd00. fix #175