New chapter on raster-vector conversions and interactions

[Robinlovelace]

From #698

Looking at it, it's a long chapter. I think that splitting out the raster-vector interactions content into a new dedicated chapter could represent a quick win, it's a long chapter and the topic is so important as to merit it's own chapter IMO atm.

It's not a definite yet but opening an issue to track progress/discussion on the topic. If anyone else has thoughts, here's the place to say.

[Robinlovelace]

This is now done: https://geocompr.robinlovelace.net/raster-vector.html