SqlTypeModifierImpl should be public

[q-litzler]

private open class SqlTypeModifierImpl(modifier: String) : SqlTypeModifier {

Should be public. This would allow the following, for instance:

val DELETE_CASCADE = SqlTypeModifierImpl("ON DELETE CASCADE")

FOREIGN_KEY("trackartist", "artist", "artistid") + DELETE_CASCADE

For those reading this issue, you can implement your own SqlTypeModifier in the meantime.

val DELETE_CASCADE = MySqlModifierImpl("ON DELETE CASCADE")

class MySqlModifierImpl(override val modifier: String = " ON DELETE CASCADE") : SqlTypeModifier {

    override fun toString(): String = modifier
}

Don't forget the very important override toString() = modifier, or else it will not work.