templatized value_t to allow calculations with complex numbers
This would also simplify issue #39 (closed) and is required for most quantum calculations.
- overloaded wrapper functions for lapacke, blas and suitesparse
- prob. two template types: value_t and real_t (return value of forb_norm eg. should not be complex)
- optionally interaction between different templatized versions (eg. Tensor with Tensor?)