Branch allowing for sqlite usage.

Hello,
I appreciate the work you've done creating this nifty little local endpoint.
The thing is, I wanted to be able to run it just using PHP's built in test server, without having a mysql server setup.
So, I created this branch.
I'd consider it an honor if you would create an sql branch, and pull my changes into it.

Sincerely,
Arthur Moore

Changes:
README.md is now more friendly to novice users.
Database format now uses unix epoch time.
Database now takes care of order uniqueness and updating.
SQL statements updated to account for changes.
PHP now converts time to unix epoch for the database.

To test:
Make sure 'orderhistory' works correctly.