Analyses a molecular formula given in String format and builds
an AtomContainer with the Atoms in the molecular formula.
About implict H handling: By default the methods to calculate formula, natural and canonical mass
use the explicit Hs and only the explicit Hs if there is at least one in the molecule, implicit Hs are
ignored. If there is no explicit H and only then the implicit Hs are used. If you use the constructor
MFAnalyser(IAtomContainer ac, boolean useboth) and set useboth to true, all explicit Hs and all implicit Hs are used,
the implicit ones also on atoms with explicit Hs.