Triazole tautomers not normalized

[jw-feng]

Hi Matt,

A disubstituted 1,2,4 triazole have three possible tautomers. I ran molvs standardize on three different SMILES and got three different answers. I don't think tautomer.py covers canonicalization of trizoles.

Here are test cases to reproduce the problem:
molvs standardize -: "CC1=NN=C(CC)N1"
output: CCc1nnc(C)[nH]1
molvs standardize -: "CC1=NC(CC)=NN1"
output: CCc1n[nH]c(C)n1
molvs standardize -: "CC1=NNC(CC)=N1"
output: CCc1nc(C)n[nH]1

Note that I got three different outputs when I expected identical outputs.

Here are structures and their respective smiles for the three different inputs.

Thanks,

JW