[MlMt] Request for "Preview at Right" mode

[Sam Hathaway]

Hi Benny and MailMate users,

I like the “Preview at Right” mode for editing Markdown emails. 
However, I’m kinda particular about the width of my compose windows 
and I don’t like that the space available for editing gets cut in half 
when I show the preview pane. I usually end up resizing the window to be 
twice as wide, but then on my next plain-text message I have to shrink 
it again.

What would be great is if I could have the window automatically double 
its width when the preview pane is shown, and halve its width when the 
preview pane is hidden. A hidden preference to turn this on would be 
fine with me.

I wonder if others might like this too. Anyway, thanks for considering 
it!
-sam