Consider Deuterium and Tritium not to be heavy elements by Element#isHeavyAtom

Update the Javadocs and fix a typo as well.
Merge pull request #45 from ulyssecarion/heavy-water

Consider Deuterium and Tritium not to be heavy elements by Element#isHeavyAtom
Add ChemCompAtoms to ChemComp
Have ChemCompConsumer respond to newChemCompAtom
Merge pull request #46 from ulyssecarion/chemcomp-atoms

Chemcomp atoms
adding some null value tests
Merge branch 'master' of github.com:biojava/biojava