Initial work on Lotus::Model.adapter
Replace Lotus::Model::Adapter with Lotus::Model::Config::Adapter
Add test for Lotus::Model.adapters
Remove #default attribute from Config::Adapter

Instead, set it to Model.adapters[:default]
Initial work on Lotus::Model::Configuration
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 }
```
Merge pull request #41 from joneslee85/issue-33

[WIP] Allow Lotus::Model to register adapter instance
Clean up test
Merge pull request #44 from joneslee85/clean-up-test

Clean up test
Move lotus model adapter into Configuration
Replace :: with .
Refactor Configuration
Not allow direct manipulation to adapters
improved checking arguments where condition

https://github.com/lotus/model/issues/42#issuecomment-50452105
Add test for Configuration
Minor clean up for Configuration test
Tweak Configuration#adapter doc
Merge pull request #45 from tguo/move-configuration-out-of-model

[WIP] Move lotus model adapter into Configuration
implemented lambda expression for exclude and or
Refactor Configuration test