hough transform for circles
add unittest for hough circle
update contrib
add blank line
various minor fixes
declare cython variables
use a single array
variable in cdef
bugfix dim + unittest
add example for cicular hough transform
Docstring + J.S. modifications
hough transform for circles
use draw instead of mpl patches
remove import mpl patches
Merge pull request #431 from sciunto/houghcircle

ENH: Add circular Hough transform.

Conflicts:
	skimage/transform/_hough_transform.pyx