v3.1.0 nonoptimal solutions

Now, along with multiple solutions, nonoptimal solutions could be obtained if desired. Example:

from ugropy import unifac

toluene = unifac.get_groups("toluene", search_multiple_solutions=True, search_nonoptimal=True)

print(toluene[0].subgroups)
print(toluene[1].subgroups)

You will obtain:

{'ACH': 5, 'ACCH3': 1}
{'CH3': 1, 'ACH': 5, 'AC': 1}

The solutions are always ordered from most optimal to less optimal.

What's Changed

• Nonoptimal by @SalvadorBrandolin in #35

Full Changelog: v3.0.5...v3.1.0