Add option to keep original resolution

[burke86]

Thanks for developing this package. I would suggest a feature in the reproject methods to keep the original pixel scale after the projection (similar to the lock frame to WCS feature in ds9). The use case would be when one wishes to align a higher resolution image to a lower resolution one while keeping all the details in the higher resolution image. I guess it would require an additional interpolation step under the hood. Or, if there is a simple way to do this, I would be glad to know.

Thanks!