Added missing documentation for torch.norm
Correct computation of L0-norm

The existing norm computation correctly computes the Ln-norm for n >= 1.
For L0, however, the result is always inf due to the presence of the 0th
root. This commit adds a special case for L0, which is computed the
conventional way: by simply counting non-zero elements.
Generalised reduceDim to transformReduceDim

This is need by some kernels to be added later.
The existing reductions are implemented in terms of this (with an
identity transformation) at no cost.
Changed parameter order of transform-reduce

... for consistency with thrust::transform_reduce.
Added reducing form of CudaTensor.norm

i.e.
	x = torch.CudaTensor():rand(5,5)
	x:norm(2,1) -- 2-norm along 1st dimension
Correct computation of L0-norm for CudaTensor.norm

Same scheme as in 9b1049fc2c8e0b087d3420a37ee32977f9b281cd
Merge pull request #131 from akfidjeland/norm

Improved norm computations