Equation references are wrong

[Overv]

The equation references in the code appear to be referring to an old version of the paper. For example, this line references an equation with a sigma:

https://github.com/atilimcetin/guided-filter/blob/master/guidedfilter.cpp#L133

However, equation 14 in the final paper does not have a sigma in it:

http://kaiminghe.com/publications/pami12guidedfilter.pdf

I think the code means to reference equation 19 instead.