Implement atleast_2d and friends

[rpadams]

http://docs.scipy.org/doc/numpy/reference/generated/numpy.atleast_2d.html

Sometimes I want a piece of code that can run on a stack of vectors. Other times I want it to work on a single vector, where I'd also like a gradient. Specific use case: I write a function handle for log likelihood. I might want its gradient, but I might also want to produce a contour plot without looping.