adding any kind of labels

[JeffersonH44]

I found that in some papers you can find something like this:

1,3,5-Tricyano-2,4,6-tris(2-dimethylaminovinyl)benzene (Leu-07)

and this is not allowed in the current grammar, so I decided to allow any kind of names at with length at least of 3 like Leu. @mcs07

[JeffersonH44]

@mcs07