- get rid of the ugly quick hack within SQL::Schema::Table->create_statement
  which eleminates system generated not null constraints as they also occur
  within user_tab_columns as attribute

- make use of schema name consistent

- support partitioned tables

- need to do more checking within SQL::Schema::Sequence->new()
  - min_value < max_value (requires BIG integer arithmetics)
  - abs(increment_by) < max_value - min_value
  - cache_size > 0
  - cache_size < max_value - min_value
  - last_number in [ min_value, max_value ]
  - sequence_name and schema_name need to consist of allowed characters

- split SQL::Schema::Constraint into several classes:
    SQL::Schema::Constraint                  as abstract class
    SQL::Schema::Constraint::Check           derived
    SQL::Schema::Constraint::PrimaryKey        "
    SQL::Schema::Constraint::Unique            "
    SQL::Schema::Constraint::Referential       "
    SQL::Schema::Constraint::VCheck            "

- fix bug within SQL::Schema::Sequence->select() introduced
  by start_with = last_number + increment_by

- support all of Oracle's attributes for a table with SQL::Schema::Table;
  currently only a very small set of attributes is supported

- support all of Oracle's attributes for a column with
  SQL::Schema::Table::Column; currently only a small set of attributes
  is supported
