Adding FileAsyncHttpResponseHandler

Hi,

I ran into issues when I tried to download big files (mp3 files). The request stopped in the middle of the download, probably because of a OutOfMemoryError. The files had size over 12Mo.

To fix this bug, I created a FileAsyncHttpResponseHandler. This handler writes directly the body of the request in a file specified by the class constructor. Like this, the ram isn't overloaded.

I based my class on the BinaryAsyncHttpResponseHandler's file.

Hope it will help!