Handle requests with ETags

[AmmarkoV]

E-Tags are very useful , and naturally fit the AmmarServer caching mechanism , they should be implemented soon..
In fact I am already on it http://en.wikipedia.org/wiki/HTTP_ETag ..

[AmmarkoV]

E-tags are almost implemented though they are not "strong" yet ..
When Range responses will get implemented I will add the last part and they will become ready..!