Update PdoStorage.php

Adding a cachedUntil field in cache table and update validateCache method to use timestamp instead wall XML to check if data still valid or outdated.
Update README.md

Update CREATE TABLE query in order to fit to last PDOStorage modifications.
Merge branch 'patch-2' of github.com:warlof/phealng into warlof-patch-2
Merge branch 'master' into development
conflict solved
Merge branch 'master' into development
code style fixes
PSR-3 compatible logger added
codestyle fixes
more style fixes
a last whitespace fix