Some changes
Improved operator framework and lbfgs implementation
Computation of standard deviation of errors in compute_mc_error
LBFGSOperator works now also with L=0, quasi_newton issues warnings
Added test for BFGS with full tensors of order 3
Extended the gpc/spde demo and renamed the tightplot function to enhance_plot
Added distribution objects and moved them to a new location
Also moved the operators to a new location under sglib/objects