def is_values(*values)
      Daru::Vector.new values.map { |v| eq(v) }.inject(:|)
    end
@note Do not use it to check for Float::NAN as
Float::NAN == Float::NAN is false
Return vector of booleans with value at ith position is either
true or false depending upon whether value at position i is equal to
any of the values passed in the argument or not
@param values [Array] values to equate with
@return [Daru::Vector] vector of boolean values
@example
dv = Daru::Vector.new [1, 2, 3, 2, 1]
dv.is_values 1, 2
# => #<Daru::Vector(5)>
#     0  true
#     1  true
#     2 false
#     3  true
#     4  true