Change indentation to spaces
Send must-revalidate directive with cache-control header
Add sending of no-cache directive if no cookie is set

If no cookie is set, there is a chance the user has JS disabled and the cookie hasn't been set by the CSS when the image is requested. Sending a no-cache directive forces the client to revalidate (not re-request) the cached image with the server.
Increment version number
Remove testing content from production code
Send 404 if image not found, option to send a retina image if it exists instead. Close #3
Add NC (no-case) flag to image regex
Convert readme to Markdown
Send status header with ability to disable
Clean up
Add option to use X-Sendfile.

close #6
Serve @2x images for @1.5x devices

Close #15
whitespace
Only run retinaimages.php when the cookie is present

Close #20
Bump version number
Add config for nginx
Merge remote-tracking branch 'upstream/master'