Use size_t for sizes
Destroy date lock as well when shutting down
Clean up some death queue-related code
It is unlikely the compression will fail
Kill request if we fail sending a response
Update TODO list, adding notes on C10M and TCP flags to try
Make sure file is closed even if coroutine is aborted

The lwan_sendfile() function can yield from the coroutine -- and it might be
killed, for instance if the connection is closed.  Using the deferred table
from the coroutine, we make sure the file is closed if the coroutine is
closed at the right moment regardless if the socket has been closed or not.
Don't give up so easily when file descriptors are scarce

This will try to open a file a number of times -- decrementing a counter
every time the process file descriptor table is full, and yielding the
coroutine at that point.  This should, in theory, give some time to free up
a file descriptor.  If that counter goes to zero, we just give up and return
a 503 (Service Unavailable) error.  All other errors (Forbidden, Not Found,
etc) as handled as usual.
Split lwan_parse_request() into smaller functions