Expose python binding for running multiple detectors at once

[thaiat]

This exposes a static method run_multiple on dlib.fhog_object_detector that accepts a list (python list) of detectors

The results have the same form as for the run method

Example:

detector_1= dlib.fhog_object_detector("object_detector1.svm")
detector2 = dlib.fhog_object_detector("object_detector2.svm")
detectors = [detector1, detector2]
retval = dlib.fhog_object_detector.run_multiple(
    detectors, 
    image, 
    upsample_num_times=0,  
    adjust_threshold=0.0)

[davisking]

Thanks, looks good except for a minor typedef thing.

[davisking]

I think you should be able to use the simple_object_detector everywhere here, so this new typedef isn't needed. It would also make it clear that all these pieces of code must operate on the same type, simple_object_detector, which I'm pretty sure is the case.

[davisking]

Awesome, thanks for the PR :)