Expand message editor in full-page size

[nu111]

What would you like to do?

I would like to have the ability to expand the message editor area to a full-page size.

Why would you like to do it?

Sometimes I need to write a non-compulsive, well thinked message, I would love to have more space to write/edit this kind of messages, that for the most are written in markdown markup.

How would you like to achieve it?

I think that a button should appear inside the one-line message editor, clicking this button should expand the message editor in a full-page text. (For pro-users I would think also to keyboard shortcut, maybe)