Add Signet Parsing by Default

[thebrandonlucas]

Simple change to add signet parsing by default. You could add custom networks as in here, but there's no reason to have it not parse signet by default. This allows packages that use this library to parse signet without refactoring

[junderw]

I think you meant to point at another fork?

[thebrandonlucas]

@junderw Apologies, yes. Here is the updated pull request with the right fork: #73