Added periodicity in heisenberg_hamiltonian_subsp and added function to get number of spins from psi.

Does blockwise diagonalization except for the subspaces of dimension 1, which still has to be implemented. Moreover, validation code needs to be written which compares with genuine diagonalization without the use of subspaces. Lastly, it would be interesting to compare performance.

I am creating functionality which makes the Hamiltonian block diagonal. Currently this is implemented by taking the total z-magnetization as a good quantum number.

Fixed bug in complex diagonalization of the hamiltonian and added periodicity for the Kagome lattice, which does not coincide with pra 42, 8436 (90)

I have added a Hamiltonian function which allows for local specification of the magnetic fields along the z-direction.

Added v2 which works for general Hamiltonians, but only for the real part. The non v2 is now broken.

I have added the kagome Hamiltonian to the file list. In order to do so, I took hamiltonian_real class apart such that it can be seperated in to functionality related to the Heisenberg Hamiltonian and functionality for general real hamiltonians. The latter is now contained in hamiltonian.h/cpp. For the complex class this is still to be taken apart

Added the ability to apply Hamiltonian to wave function, and cmake falls back on lapack when MKL is not available