schema-qualified table names result in broken struct names in identity mode

[rbock]

From #106, thanks @MeanSquaredError :

arguably there is a bug in the way ddl2cpp handles schema qualified table names when --naming-style identity is enabled. In that mode this definition

CREATE TABLE mysc.mytbl (
myid bigint NOT NULL
);

will generate a header which looks like this :

struct mysc.mytbl_ {
struct myid {
SQLPP_CREATE_NAME_TAG_FOR_SQL_AND_CPP(myid, myid);
using data_type = ::sqlpp::integral;
using has_default = std::false_type;
};
SQLPP_CREATE_NAME_TAG_FOR_SQL_AND_CPP(mysc.mytbl, mysc.mytbl);
template
using table_columns = sqlpp::table_columns<T,
myid>;
using required_insert_columns = sqlpp::detail::type_set<
sqlpp::column_t<sqlpp::table_t<mysc.mytbl>, myid>>;
};
using mysc.mytbl = ::sqlpp::table_t<mysc.mytbl>;

This is clearly broken because struct mysc.mytbl_ and using mysc.mytbl are obviously incorrect definitions. However this can be fixed relatively easily by fixing ModelWriter._to_class_name and ModelWriter._to_member_name, which currently replace . with _ in camel-case mode, but incorrectly don't make that replacement in identity mode.