Add DMRG-3S algorithm

Add a faster version of the DMRG-1 site algorithm that prevents from falling into local minima. The algorithm is described in https://arxiv.org/abs/1501.05504

2-site DMRG algorithm

Added the 2-site version of the DMRG algorithm

Basic 1-site DMRG algorithm

First basic release of the Matrix Product States with a functioning simple 1-site DMRG algorithm for finding ground states of lattice Hamiltonians.