BUG: Set operators are inconsistently handled

[martinfleis]

Fixes #81

Set operators currently worked on GeoSeries but not on GeoDataFrame.

a = GeoSeries(...)
b = GeoDataFrame(...)

a.intersection(b)  # Okay
b.intersection(a)  # Okay
a & b  # Okay
b & a # Error

GeoDataFrame now supports operators as well using its geometry column.

[jorisvandenbossche]

Question: do you personally use those operators?
I personally never have done that, and I find the methods also much more explicit (I have thought in the past to open an issue about this, to potentially deprecate it)

The PR itself looks good though!

[martinfleis]

do you personally use those operators?

I don't. It is a bit confusing to understand what they do. But I can imagine some people may use them. I was just going through old issues and seen this, which was quite easy to fix.

I think there is no harm having these as a shortcut for intersection etc., if someone likes using operators.

[martinfleis]

Now we have consistent behaviour of set operators between GeoDataFrame and GeoSeries. We can still decide to deprecate it altogether.

[jorisvandenbossche]

Personally I would deprecate them. Let's start with opening an issue for that?

[martinfleis]

I'll do a quick PR straight away.