Allow vim-style magic encoding comments
Merge pull request #468 from meatballhat/accept-vim-style-encoding-comments

Allow vim-style magic encoding comments
Split VariableInspector inner classes into multiple files

Also rename VariableEntry to Variable.
Track usage of each assignment in UnusedLocalVariable

The cop now tracks usage of each assignment
rather than usage in entire variable lifetime.

This closes #458.
Fix crashes at class definition subclassing class stored in a lvar
Reorganize UnusedLocalVariable and UselessAssignment

* Extracted useless setter call tracking part of UselessAssignment to
  UselessSetterCall.
* Renamed UnusedLocalVariable to UselessAssignment.