This extension for the CMB2 custom metabox framework introduces a dedicated field type for writing and editing content in Markdown syntax. It is designed for developers building custom admin interfaces who need to provide a clean, structured writing experience for content editors.

• Markdown field type: Adds a new text_markdown field type to the CMB2 library, enabling the use of Markdown formatting directly within custom metaboxes.
• Integrated sanitization: Includes a markdown_sanitize callback function to properly process and secure the Markdown input data.
• Simple implementation: The field is defined using the standard CMB2 add_field method, maintaining consistency with the existing framework workflow.
• Structured content output: Allows editors to use Markdown for lists, headers, and emphasis, which can then be rendered as HTML on the public-facing site.