Revert "Add metabox inside post"

This reverts commit ce0f555820ec5934d49adb15ec3e11f75da5d84c.
Revert "Revert "Add metabox inside post""

This reverts commit fdf59cb82a0362df6b2b3875c5958d90f4ed7134.
Add markdown.md
Merge remote-tracking branch 'origin/master'