scale and offset issues

[mdsumner]

• [ ] gdal_raster_io doesn't apply scale/offset
• [ ] currently, scaling overrides the _int type request
• [ ] allow user set "scale = TRUE"
• [ ] defaults: return native type, return float64 if scale/offset present
• [ ] if type is specified return that
• [ ] if scaling is turned off just ignore it

(don't have entire clarity on this rn, currently _int returns scaled floats, though)

and see 31c386e

[mdsumner]

currently working towards pulling the band-reader stuff out of the warper function, it might make sense to create a function for each R type and only do scaling in the float64 one, and allow that to be turned off

because, really the curent rasterio stuff should be called by the warper function from an open dataset

[mdsumner]

• [ ] (perhaps) provide GetScale and GetOffset