Added Content-Length to the Response
This now counts the string length of the response body and outputs
the Content-Length header accordingly.

Signed-off-by: Tom Schlick <tom@tomschlick.com>
switched to  multibyte length function (mb_strlen)

Signed-off-by: Tom Schlick <tom@tomschlick.com>
Checking if mb_strlen exists first

fall back to strlen
using MBSTRING
Merge pull request #1261 from tomschlick/request-content-length

Added Content-Length to the Response