Backend-agnostic connections

[flying-sheep]

I’d like to create a impl Connection for PgOrSqliteConnection or at least a Box<Connection> but the former requires me to implement dozens of interfaces and the latter is impossible due to the associated Backend type.

[sgrif]

Connections aren't object safe, and basically never will be able to with Rust as it is today. You'll have to write your functions as fn foo<T: Connection>(conn: &T)