fix and extend documentation
fix argument processing in DescriptorMatcher knnMatch/radiusMatch

the following two calling forms were incorrectly processed:
    matcher.knnMatch(qryDesc, k, 'Option',val, ..)
    matcher.radiusMatch(qryDesc, mxDist, 'Option',val, ..)
fix variable types and default values to match those in OpenCV sources
explicitly cast mask as logical
add LSH Flann-based indexer to DescriptorMatcher