Besides the common `:param` notation to designate named parameters in
prepared statements, SQLite3 also supports `@param` and `$param`.
While the latter is mostly to support the Tcl programming language, and
would be confusing for PHP's sqlite3 binding due to the similarity with
string interpolation, the former is common under .NET and raises no
such issue. Therefore we add support for it.
This patch has been developed in cooperation with @BohwaZ.
