Finding indices and number pixels for rectangle shapes

This module will find the indices of rectangle or square shape and count the
  number of pixels in that shape.

Use slice objects here so tis is readable

```python
slc1 = slice(np.max([x_corr, 0], np.min([x_coor + x_val, max_cols])
slc2 = slice(np.max([y_corr, 0], np.min([y_corr + y_val, max_rows])
```