f64/d2/vec.go
func (v Vec) ApproxEpsilon(v2 Vec, threshold float64) bool {
	if !f64.ApproxEpsilon(v.X, v2.X, threshold) {
		return false
	}
	if !f64.ApproxEpsilon(v.Y, v2.Y, threshold) {
		return false
	}
	return true
}
func (v Vec) ApproxEpsilon(v2 Vec, threshold float64) bool {
	if !f64.ApproxEpsilon(v.X, v2.X, threshold) {
		return false
	}
	if !f64.ApproxEpsilon(v.Y, v2.Y, threshold) {
		return false
	}
	return true
}
// ApproxEpsilon reports wether v2 is approximately equal to v, using provided
// epsilon value.
//
// Element-wise approximation uses f64.ApproxEpsilon()