Class::DBI::Loader automate the definition of Class::DBI sub-classes. scan
table schemas and setup columns, primary key.

class names are defined by table names and namespace option.

+-----------+-----------+-----------+
|   table   | namespace | class     |
+-----------+-----------+-----------+
|   foo     | Data      | Data::Foo |
|   foo_bar |           | FooBar    |
+-----------+-----------+-----------+

Class::DBI::Loader supports MySQL, Postgres and SQLite.
