Refactor `AbstractSearcher` class and its children. Also most of the
unnecessary logic that was on `AbstractSearcher` was put back into `In`
class.
This commit also updates all "SubdivisionCode" rules.
The script used to create the classes can be found on:
https://gist.github.com/henriquemoody/ec404f994a87b18c7771
- Move "tests/phpunit.xml" to "phpunit.xml.dist"
- Update documentation and contributing documents
- Update Travis settings
- Add "phpunit.xml" in the Git ignore list