Re-edited the documentation again.

Attempting to re-editing the documentation, to satisfy buildbot error
status.

Edited previous code to change tabs into spaces.

Added a method "loadFromString" which is based on the "load" one. It
allow to directly pass the XML string which can be usefull and faster
when you have a huge file in a variable.

There is necessary to account also x-coordinate of the end of the edge when determining bounding box of the edge collection.

- Use cv::AutoBuffer rather than new allocation
- Fix "assignment operator could not be generated" warning

mask = cv2.inRange(hsv, lower_green, upper_green)
to
mask = cv2.inRange(hsv, lower_blue, upper_blue)