unlock the required version of symfony/polyfill-php70

update CHANGELOG.md for v0.9.8

updated CHANGELOG.md and README.md

updated CHANGELOG.md

added CHANGELOG.md and updated README.md

update README.md with Known Caveats section

address issue #3: avoid calling session_regenerate_id from inside the…

… handler to make it compatible with PHP 7.1.2+

address issue #3: handler does not work on PHP7+

address issue #1: spinlock should usleep

initial release