Use String as key

1.9.3はsymbolとstring両方で取れるが、2.0.0はstringでしか取れない
両方で使えるように、stringで取る
Ruby2.0.0ではValueがStringでないと保存されない
Merge pull request #184 from sanemat/feature/option-restore

Ruby2.0.0でOptionのsave, restoreが出来るようにした
Add redcarpet.
Merge pull request #185 from hrysd/redcarpet

Add redcarpet.
Add default markup in admin/site/edit
Merge pull request #187 from rono23/add-default-markup

Add default markup in admin/site/edit
Upgrade sinatra, rake and rack
Remove ruby 1.8.7 support
Add ruby2.0 support
Remove waste file
Fix preview
Merge pull request #189 from rono23/fix-preview

Fix preview
Merge pull request #188 from hrysd/remove-waste-file

Remove waste file