add codecoverage  & add french word in str_to_bool & add an array_clean

Hello,
Some features : 

* A coveralls.io integration [![Coverage Status](https://coveralls.io/repos/lilobase/utilphp/badge.png?branch=master)](https://coveralls.io/r/lilobase/utilphp?branch=master)
* A new `array_clean` function, it remove all false/null/empty values from the given array
* Add french words (oui = yes, non = no) in the `str_to_bool` function