Bug Fixes client: coerce HTTP_2 requests to HTTP_11 (3a6080b1, closes #1770) http2: send INTERNAL_ERROR when user's Service errors (8f926a0d) Features error: implement Error::source when available (4cf22dfa, closes #1768) http2: Add window size config options for Client and Server (7dcd4618, closes #1771) server: add http2_max_concurrent_streams builder option (cbae4294, closes #1772) service: add poll_ready to Service and MakeService (#1767) (0bf30ccc) allow FnMut with service_fn (877606d5)