added where condition in code block

Sequel already has an option to define you condition in a code block,
like this:

```ruby
UserRepository.where{ age > 31 }
```
improved checking arguments where condition

https://github.com/lotus/model/issues/42#issuecomment-50452105
implemented lambda expression for exclude and or
Added examples and fixed typo
removed puts in test
Merge pull request #46 from coenert/master

added expressions to where condition