Created ability to return specific column data

Create new core method  to return specified columns in an adapter independent manner. 

<b>Example 1:</b>

model.select({where : {name: 'bill'}, attributes: 'id'}}, callback)
OR
model.select({attributes: 'id'}}, callback)

<i>returns array of ids (e.g. [ 1, 2 ])</i>

<b>Example 2 :</b>

model.select({where : {name: 'bill'}, attributes: ['id']}}, callback) 
OR
model.select({attributes: ['id']}}, callback)

<i>returns array of objects(e.g. [{id: 1}, {id: 2}])</i>

<b>Example 3:</b>

model.select({where: {address: '123'}, attributes: ['id', 'name']},callback) 
OR
model.select({, attributes: ['id', 'name']},callback)

<i>returns [{id: 1, name: 'bill'}, {id: 2. name: 'alice'}]</i>