add has many associations functionality
Revert "Fix Travis Shields.IO image" [ci skip]

This reverts commit 214433575f6748ba9d9504126b96dcb64662b151.
fix bugs and change alias to alias_method
fix bugs
Merge https://github.com/airblade/paper_trail into has-many-associations
Merge pull request #1 from lyfeyaj/has-many-associations

add has many associations functionality