Basic img_proc module revision and re-org using API option

Reorganized the thresholding, histogram, morphology and filter operations so that all direct imports are removed and now loaded via the api.

Remaining tools to follow.
You can also do this as
```python
"thresh_value = {}, array maximum = {}, "
"resulting array fill value = {}".format(
thresh_value, np.amax(src_data), True))
```

i.e., without the numbers in the parenthesis.

Note that I'm not suggesting you **should** do this, just mentioning you can also do it without the numbers