* - optimization to UFF and MMFF forcefields
* - further optimizations (memset, factoring unnecessary in-loop
initialization out of the loop, replacing if clause with pre-increment)
* - fixed a couple of stylistic glitches
* - the torsionSmarts parameter in addTorsions() is now a const std::string&
* - implemented the DefaultTorsionBondSmarts singleton using boost::call_once()