code: @Override
      public boolean matches(IAtom atom) {
          // h counts should be set before match throw runtime exception?
          if (atom.getImplicitHydrogenCount() == null)
              return false;
          return atom.getImplicitHydrogenCount() == hcount;
      }
docs: /*
  (non-Javadoc)
  @see
  org.openscience.cdk.isomorphism.matchers.smarts.SMARTSAtom#matches(org
  .openscience.cdk.interfaces.IAtom)