Better string interpolation

The standard String Interpolation (e.g. `s"some $string interpolation"`) can be mixed with Anorm one.

```scala
val cmd = "SELECT"
val table = "Test"

SQL"""#$cmd * FROM #$table WHERE id = ${"id1"} AND code IN (${Seq(2, 5)})"""

// prepare the SQL statement, with 1 string and 2 integer parameters:
// SELECT * FROM Test WHERE id = ? AND code IN (?, ?)
```
String interpolation specs