several changes see comment

**Important changes:** 
- __BC break__ changed ini setting ```excel.ini_skip_empty``` to ```excel.skip_empty``` 
- removed ```ZEND_ACC_FINAL``` for ```ExcelFormat::__construct()``` 
- changed ExcelBook::__construct() 

**Minor changes:** 
- replaced several spaces with tabs 
- added test 084.phpt for issue #86 
- fixed test 064.phpt 
- updated README 
- updated / changed formatting changelog 
- applied [php-cs-fixer](http://cs.sensiolabs.org) --all}} for docs/*.php 
- updated docs