Postgres `$` dollar placeholder support.

[gmhafiz]

The library isn't able to parse postgres query with $ placeholders.

tree, err := sqlparser.Parse("INSERT INTO users (email, name) VALUES ($1, $2)")
if err != nil {
    fmt.Println(err)
    // err = syntax error at position 52 near '$'
}

I can see the variable yyDollar being used so not sure if this dollar placeholder is supported or not.