UNIQUE
UNIQUE = 'unique' : string
setColumns(array  $columns) : \Phinx\Db\Table\Index
                Sets the index columns.
| array | $columns | 
setType(string  $type) : \Phinx\Db\Table\Index
                Sets the index type.
| string | $type | 
setName(string  $name) : \Phinx\Db\Table\Index
                Sets the index name.
| string | $name | 
setLimit(integer  $limit) : \Phinx\Db\Table\Index
                Sets the index limit.
| integer | $limit | 
setOptions(array  $options) : \Phinx\Db\Table\Index
                Utility method that maps an array of index options to this objects methods.
| array | $options | Options  |