C# API

[nblumhardt]

I want to use Piggy programmatically for a quick-and-dirty F5 deploy/run experience. This PR exposes the minimal types needed for this:

// dotnet add package Datalust.Piggy
var connectionString = // Npgsql connection string
using (var connection = DatabaseConnector.Connect(connectionString))
{
    UpdateSession.ApplyChangeScripts(connection, "./db", new Dictionary<string, string>());
}