I also used this feature in the past, and am disappointed to see it gone. It was convenient to be able to "draw" onto the chart for common navigational tasks. These were things I'd plan once and have on the chart indefinitely in the future to save redoing it again on future flights.
The file format seems straightforward though, looking at what I already have from older versions. It looks like this:
[Name of route|Notes with spaces]
N123456.78 W00123456.78,2000,3000,1,VFR,U
N123456.78 W00123456.78,2000,3000,1,VFR,U
... (more lines for more legs)
N123456.78 W00123456.78
[Name of another route|its notes]
N123456.78 W00123456.78,2000,3000,1,VFR,U
N123456.78 W00123456.78,2000,3000,1,VFR,U
... (more lines for more legs)
N123456.78 W00123456.78
The final point on each route doesn't specify any properties for the subsequent leg, of course. It's a text file formatted with Windows line endings. I don't remember what the 1,VFR,U means above. Those are the settings I used previously. I'd appreciate if you could fill us in, please!
The editor previously didn't let you do this visually; you had to enter in lat/lon manually - essentially the same information as above.