Compilation error when Scalar is Eigen::half and not float #346

Since class Matrix is templatized

template <typename Scalar>
class Matrix final {
......
 private:
...........
  // The zero_point, i.e. which Scalar value is to be interpreted as zero.
  // When Scalar is floating-point, this must be 0.
  Scalar zero_point_ = 0;
};

I could have something like: Matrix<Eigen::half> myMatrix;

but then at compilation I get error: no viable conversion from 'int' to 'Eigen::half' Scalar zero_point_ = 0; since the zero isn't templatized

integer 0 and float zero are interchangeable so the above code works; but it's not the generic case for templates. I believe an implementation like Scalar zero_point_ = Scalar{0}; is more generic

Similar fixes to other classes and parts of the code?