New command: cmd_md

[easyrider]

Save the last assistant message to a specified file and directory.

When you run the /md test.md command, it will save the file to the notes directory inside the project root.

Example Usage:

• If the user runs /md my_note.md, the file will be saved to /notes/my_note.md.
• If the user runs /md /path/to/notes/my_note.md, the file will be saved to the specified path.

[CLAassistant]

All committers have signed the CLA.

[golergka]

I think this is somewhat related to this issue of mine: #2777

May be we should work on a more generalistic logging tools?