When ClientTimeSpan is 0 and MustRevalidate is false, then there is no CacheControl header.
When ServerTimeSpan is 0 then the response in not stored in the webcache.
Removed ServerTimeSpan from CacheTime as it was not used anywhere.
Merge pull request #12 from rjvdboon/AllowClientTimeSpanZeroAndServerTimeSpanZero

Reenable ClientTimeSpan zero and ServerTimeSpan zero