[-] FO: Turns off output buffering

Previously if output buffering was on and there was 0 length in current
buffer output buffer would stay on. This fix turns off output buffering,
because it causes problems when downloading large files, PHP crashes due
to memory limitations
[+] FO: added support for download resume

When downloading large files it's crucial to be able to resume download
if connection temporarily fails.
Added support for HTTP_RANGE header and resumes download where you left
off, by seeking to correct location.