quick fix for save_hdf codes

[jalew188]

save_hdf in the library classes by using:

_hdf.library = {
    'precursor_df' = precursor_df,
    'fragment_df' = ....
}

[jalew188]

#3 comments by @swillems

Even better: this should work as well:

_hdf_lib.decoy = {
        "precursor_df":  self._precursor_df,
        "fragment_mass_df": self._fragment_mass_df,
        "fragment_inten_df": self._fragment_inten_df,
}

[swillems]

Looks good