start making the PDB parser somewhat more robust
start making the PDB parser somewhat more robust

We now do the following:
- in case no element is provided, guess element from atom
  name. Since it's only a heuristic, this won't be 100% percent
  accurate but it should work for the most common cases.
- in case no residue number (!) is provided, default number
  to 1. Before the residue number was set to NaN and resulted in
  a new residue being created for every atom because NaN != NaN.

biasmv/pv,biasmv/pv,Traksewt/pv,Traksewt/pv,CyrusBiotechnology/pv,biasmv/pv,yuhangwang/pv,Traksewt/pv,yuhangwang/pv,CyrusBiotechnology/pv,Traksewt/pv,yuhangwang/pv,CyrusBiotechnology/pv,yuhangwang/pv,CyrusBiotechnology/pv,biasmv/pv