Use ArrayIterator instead of ArrayObject.

Simpler and better performance.
Fix typos in API documentation.
Fix a typo in the API documentation.
Fix API documentation.
Fix API documentation.
Update to PHP5.4 and format code…

… it means:
  * remove `array()` and use the short-syntax instead,
  * align some operators for consistencies,
  * remove some useless `else` branch.
Use `floatval` instead of a closure. #performance
Merge pull request #162 from Hywan/code_review

Code review