can change a path of sqlite file.

If you want to change a path of sqlite file, set the path by AppDelegate#sqlite_path= before first access to AppDelegate#managedObjectContext.

```ruby
class AppDelegate
  include MotionDataWrapper::Delegate

  def application(application, didFinishLaunchingWithOptions:launchOptions)
    sqlite_path = "/path/to/your/sqlite/file"
     .
     .
   end

end
```
Merge pull request #4 from katsuyoshi/store_path

Store path
Travis CI integration
Added rake to Gemfile for Travis CI
add callbacks and fix new_recode? still true after saved.

I add callbacks before/after_create/save/update/destroy if it exists an instance method.
Not implemented specify by a class method.

I found a bug, new_recode? still true after saved.
clear cache for test

clear @_metadata
Merge branch 'callback' of github.com:katsuyoshi/motion_data_wrapper into callback