Function to save out a mask as a geotif

[k034b363]

It would be useful to be able to save out a mask from plantcv segmentation steps while retaining the georeference information from the original image. Some possible methods of analysis, like rasterstats.zonal_stats, require a file as input, and it is also nice to have the option to save intermediate steps in long workflows.

The proposed function would take a file path to the original image, file path to a shape file if the image was cropped during read_geotif, and an output file path. Detection of whether the mask was rgb or binary could happen programmatically, because a couple of steps would change between those options.