General:
- Completed location support and added related unit tests
- Added API for future support of tab widths
Details:
- Removed PPI::Element::_line
- Removed PPI::Element::_col
- Fixed bugs in PPI::Document::index_location
- Fixed bugs in PPI::Element::location
- Added 12_location.t unit test
- Added PPI::Document::tab_width method
- Added PPI::Normal::Standard::remove_useless_attributes
(to remove the ->{tab_width} attributes and later other things)