Added new implementation of getRadius(AminoAcid, Atom) that does not
need parsing the vdw.radii file
Reimplemented AtomRadii, removing need for the vdw radii naccess file. 
Atom objects do not store their vdw radii anymore. However that adds a
significant overhead to Asa calculation since right now there's a lookup
of the atom radius at every getRadius call in Asa.
Asa calc no performs as before: radii are only looked-up once per atom
Asa is now AsaCalculator and not static anymore
Reimplementation of multi-thread ASA calc by using ThreadPool
perhaps performs very slightly worse than before, but with a cleaner
implementation
Improved scaling test and docs
Some more docs and comments
Minor doc correction