Added draft of doc
Added ising2d test for statistics...
Fixing mistake: was taking next-nearest-neighbors...
Further work on ising2d test. Added output.
Statistical tools documentation, c'ed.
Added constructor of observable on binned_series
Made autocorrtime calculation from binning faster.

Bin size is doubled at each step to converge faster and reuse previous binned series.
Added tests for alps-triqs comparison (not to be compiled, but for reference)