Allow to set addition, replacement and deletion costs by function parameters

[Darker]

Currently, the algorithm sets the same cost for addition, removal and replacement:

            current[ m_idx ] = Math.min
              ( previous[ m_idx ]     + 1   // Deletion
              , current[  m_idx - 1 ] + 1   // Insertion
              , previous[ m_idx - 1 ] + 1   // Subtraction
              )

But in my case, I'd like to make deletions and subtractions more expensive than insertions. General solution would be to have function that takes 3 more parameters:

function Levenshtein(string_1, string_2, deletion_cost, insertion_cost, subtraction_cost) {...}

Does this make any sense? If it does, would my commit that adds this feature be accepted.