syncdraw: Allow setting of @variables and flopping modes

It's hard to edit a menu when you use @variables since you cannot tell where the layout will be exactly.

There is no other editor that would have this feature and I think it'd be invaluable.

If I could set values like SYSOPAVAIL, PAGER ALERTS or whatever I wanted to match @SYSOPAVAIL@ @PAGER@ and the like in my menu file.

Then have an option to display the parsed screen that'll take into account formatting such as |L5 and hotkeys into single characters. Basically turning @(C)@hat to (C)hat

This would allow the sysop to view the finished article without having to keep saving and reviewing on the BBS.