pass xlim/ylim to sliceImage() #61

hi,

thank you for maintaining Cardinal!

when subsetting a MSImagingExperiment based on pData (like in subset <- HnE_annot[,pData(HnE_annot)$HnE_annot== annot]), the resulting field of view is cropped (if annot defines an inner/smaller region of the data).

It would be great to have the option to pass xlim and ylim (or analogous param) to either subsetPixels() or sliceImage() so that x and y lims can be manually defined or inherited from the full dataset (HnE_annot in this dummy example).

thanks!