histogrammar/histogrammar-python: 1.0.3

Adds scalar multiplication to reweight filled aggregators. (Multiplying an aggregation tree by a scalar factor has the same effect as filling with weight * factor would have. In particular, multiplying by a non-positive number is equivalent to zero.) For ROOT filling, now only reading TBranches from the file that will be used (big I/O streamlining). Tests ROOT reading from TChains (no changes were required)