Fixed database column stubs initialization code.
Replaced explicit source file declarations with auto loading.
Created unit tests for ColumnLengthValidator class.
Completed ColumnLengthValidator. Covered it by unit tests.
Created DefaultContstraintValidator class checking default constraints for data columns.
Implemented specs for default constraint validator class.
Added default_value property to DataColumnSchema class returning default constraint value.
Implemented default constraint validator for data columns.
Corrected default constraint value for [version] data column in timestamps.
Fixed incorrect default constraints in [employee] data table definition.
Fixed typo in default constraint validator message.
Defined the set of data tables with ruby based metadata.