weigh_and_bin: Weigh and sum into bins.
In myllym/marksummary: Calculate summary functions for marked point patterns

Weigh the value of the f-function for each pair, sum together results of the same bin and place the sum in the correct bin.

1	weigh_and_bin(f_value, weight, idx_vec, n_bin)

`f_value`	A vector of values from the mark test function corresponding to each pair of points.
`weight`	A vector of weights for each pair of points.
`idx_vec`	A vector of bin indices to guide each pair of points into the correct bin.
`n_bin`	The amount of bins that the returned vector should have.