def add other, opts={}
          v2v_binary :+, other, skipnil: opts.fetch(:skipnil, false)
        end
Add specified vector.

@param other [Daru::Vector] The vector thats added to this.
@param opts [Boolean] :skipnil if true treats nils as 0.

@example

v0 = Daru::Vector.new [1, 2, nil, nil]
v1 = Daru::Vector.new [2, 1, 3, nil]

irb> v0.add v1
=>  #<Daru::Vector(4)>
0   3
1   3
2 nil
3 nil

irb> v0.add v1, skipnil: true
=>  #<Daru::Vector(4)>
0   3
1   3
2   3
3   0