Update dependency versions in composer.json
update docs
Avoid race condition on cache/session updates
rewrite with bindVars syntax
improve syntax for on-duplicate-key, and rewrite to bindVars syntax
Merge pull request #242 from drbyte/index-doc

update docs in index.php
Merge pull request #243 from drbyte/composer

Update dependency versions in composer.json
Merge pull request #244 from drbyte/race-cond

Handle race condition