Adjusted parameters and added image_diff_squared (#462)

* Added blob_detector

* fixed image_array declaration

* Changed nearest neighbors to points instead of indices

* import atan2

* import pi

* Working prototype blob_detection.

* Demo change_detection.blob_detector functionality

* Updated documentation n_sigma -> num_sigma

* Addressed PR reviews.

Added returns to docstring.
Added configurable additive / subtractive change detection + docstring
Moved nested function to top.

* Added function description + citation to docstring

* Added new diff function, modified default parameters

* Removed unused num_sigma

* Added additional blob_log parameters

Co-authored-by: Austin Sanders <arsanders@ugs.gov>