Consider implicit hydrogen counts in getNaturalExactMass.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Consider implicit hydrogens in exact mass utility.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Consider implicit hydrogens in natural abundance utility.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>