Implement like operator

Added LIKE operator.

```
_foo.all({where:{name:{like:'%test%'}}},function(){});
//SELECT * FROM foo WHERE name like '%test%'

_foo.all({where:{name:{like:'test%'}}},function(){});
//SELECT * FROM foo WHERE name like 'test%'

_foo.all({where:{name:{like:'%test'}}},function(){});
//SELECT * FROM foo WHERE name like '%test'

_foo.all({where:{name:{nlike:'%test%'}}},function(){});
//SELECT * FROM foo WHERE name not like '%test%'
```