Supporting additional Charsets

[jnd71]

From #72 , @jeremyrsmith raises a question about supporting additional Charsets for Postgres. Currently we are locked in to StandardCharsets.UTF_8 throughout the code base.

Postgres gives us the current encoding of the Server through a Parameter Status update which can come at any point during the connection.

The question I have going forward - is this something we should automatically detect from Postgres and attempt to make it transparent to a user? Or should we set the encoding through Stack.Param configuration and immediately close the connection if the encoding ever changes from the Server?

[jeremyrsmith]

I think a good first step would be to proliferate a Charset everywhere that decoding needs to be done. For now we could just hard-code StandardCharsets.UTF_8 in those positions, but having them available and used inside decoders will make it possible to support dynamic Charsets either by reading it from the server or allowing the user to specify it.