Great stuff - thanks for extending the functionality to include recent extension methods.
I started working with the library, only using Postgresql. I began writing my own PostgresExecutor, only to realize that if you change one thing, it should work with either:
In SqlExecutor, you require a SqlConnection to be passed in which only works with SQL Server. Why not pass in an IDbConnection? This lets me (a Postgresql+Dapper user) pass in whatever connection I have constructed, and the next guy (A MySql user) to pass in his connection.
Unless I am missing something big, IDbConnection has the same methods available from Dapper as SqlConnection (and as NpgsqlConnection, etc...).