WIP: finding the q rings - num pixels, edge values and indices
TST: added a test to find the indices of the required Q rings, find the bin
    edges of the Q rings, and count the number of pixels in each Q ring.
DOC: updated the documentation
STY: style fixed with pep8
ENH: changed finding the way of q_ring_val
BUG: now q_val can handle (N, ) shaped arrays as well as (N, 1) shaped
DOC: modified the documentation for q_val
STY: style fixed with PEP8
BUG: taken out unwanted lines
ENH: simplified the way of finding the Q indices by using a mask