Rework maths operators
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add unit test for mln/core/image/view/maths operators -
add missing maths operators: dot, cross, min, max, l2dist_sqr, l2dist, l2norm_sqr, lpnorm, lpdist -
add missing documentation -
investigate gcc compile error -
add mln::channel, mln::red, mln::green, mln::blue (migrate code + doc)
fixes #52 (closed) #53 (closed)