Handle ConnectionReset+ConnectionAbort at any time (#168)

Previously we had a special case for BadStatusRead that would happen
only when we got a ConnectionAborted error reading the status line.
However, sometimes we get ConnectionReset instead. Also the HTTP
spec says that idempotent requests may be retried anytime a connection
is closed prematurely.

The change treats as retryable any ConnectionAborted OR ConnectionReset
error while reading the status line and headers. It removes the special
case BadStatusRead error.

Fixes #165 (I think).

src/response.rs

@@ -476,10 +476,7 @@ impl Response {
     fn do_from_read(mut reader: impl Read) -> Result<Response, Error> {
         //
         // HTTP/1.1 200 OK\r\n
-        let status_line = read_next_line(&mut reader).map_err(|e| match e.kind() {
-            ErrorKind::ConnectionAborted => Error::BadStatusRead,
-            _ => Error::Io(e),
-        })?;
+        let status_line = read_next_line(&mut reader)?;
 
         let (index, status) = parse_status_line(status_line.as_str())?;