Multi-template-matching

Added
- Checking if all templates fit in the search region/image as suggested by insertscode
- Corresponding tests

Changed
- Renamed requirements.txt to old_requirements.txt, and removed MTM from requirements. Binder uses setup.py anyway.

Added
- support mask for matchTemplates and findMatches as in cv2.matchTemplates with method 0 or 3
- notebook tutorial with mask
- CHANGELOG.MD

Changed
- better docstrings

Fixed
- issue when no detection found (see Changed of version 1.5.3.post2)

Changed
- NMS is now using the opencv `cv2.dnn.NMSBoxes` function
- use timeit for benchmark in example notebook

Removed
- `MTM.NMS.Point_in_Rectangle` and `MTM.NMS.computeIoU` as they are not used anymore for the NMS

Fixed
- issue when no detection found (see Changed)

Changed
- `MTM.findMatches` return a dataframe with proper column names (not just empty)
- better handle the different opencv matchTemplate methods

Removed
- remove the hardcoded version requirement for opencv-python-headless in setup.py

Added
- MTM version is now defined in a dedicated version.py file