Merge pull request #10 from mlewe/master

 Add a .gitignore
Fix bug in correlation_length(). sort() sorts complex values by the real part (and then the imaginary part), so avoid this by working soley with the magnitudes.
Make fidelity_per_site work with states with different bond dimensions.
Also add a dense mode for small bond dimensions.
Implement an improvement to the CG code suggested by Jutho.
Use the gradient to minimize the energy in the CG direction when the energy becomes too imprecise.
Remove NUM_ITR debug from CG.
Fix some comments in the examples.
Add a truncate option to load_state.