GeoImage functions: new vs inplace

[matthewhanson]

The convention for operations on a raster is that a new raster gets returned with the operation chained to it. Thus:

newband = band * 5

where (band * 5) returns a new GeoRaster with a x5 function added to it's chain.

In contrast, some GeoImage functions (eg AddMask) actually operate on *this, which is then returned. This is not consistent.

I think the best way is to always return a new object, that way any previous references will still contain the original GeoImage without the processing applied, which would be desirable.

Somewhat related is the various Set functions: SetGain, SetBandNames which return void and operate on *this as well, however I think with a 'Set' functions this would be the expected behavior. Although, at least returning *this from these would allow those functions to be included in a chain, e.g.,

image2 = image.SetGain(1.0).autoscale(args)