Add posibility ot setup linger option of AnyEvent::Handle object

This option is in effect when, for example, code terminates connection
by calling "disconnect" but there are ongoing operations. In this case
destructor of underlying AnyEvent::Handle object will keep the write
buffer in memory for long time (1 hour by default). If the amount
of sending data is big it causes severe memory leak.
Merge pull request #1 from ikruglov/master

Add posibility ot setup linger option of AnyEvent::Handle object