Changed the 180 constant in bin calculation to avoid rounding errors

The code
   180 / orientations
performs integral division in python < 3,
leading to the calculations ignoring some orientations near the 180 maximum
Added partial implementation of censure for mode=DoB
Line Suppression of the response
Correcting import for a private function
Adding TODO's
Added mode Octagon using np.convolve
Correcting typo
For loop for mode=DoB in Cython
Commenting out _filter_using_convolve
Removing time() statements and correcting types in censure_cy
Removing hard-coding in censure_keypoints()
Returning keypoints with the scale info
Correcting the expression of response in censure_keypoints()
Correcting the definition of Ratio of Principal Curvatures
Adding _slanted_integral_image. Removed _oct and _filter_using_convolve
Removing unused stuff
Cleaning up the non-Cython version for mode=Octagon
Cythonizing the for loops
Adding the docs for censure_keypoints
Trying to resolve Cython TypeErrors