fastinterpcol - Fast 1D interpolation along column dimension

This is an expansion of the interp1q function of Matlab, aiming to improve the speed for 2D interpolation by using vectorization.

The Matlab's built-in `interp1q` function is known to be a very fast linear interpolator that can deal with non-uniform grids. However, it only supports 1d input vectors. Interpolating over multiple columns of a 2D matrix will require multiple calls of `interp1q` using the for loop, which is very slow.

This source code implements `fastinterpcol`, a vectorized version of `interp1q`. This function does very fast interpolation along the column dimension of a 2D matrix. Interpolation along the row dimension can be also done simply by transposing the input before calling the function.

Experimental results show that `fastinterpcol` is at least 2x faster than `interp1q` for a matrix of 100 columns.