Several stop-sending bug fixes; new optional callback

• [BUGFIX] Do not drop incoming data when STOP_SENDING is received.
• [BUGFIX] Receipt of STOP_SENDING should not cause read-reset.
• [BUGFIX] Allow stream writes after receiving RESET.
• [BUGFIX] Typo in stream: ANDing enum with wrong flag.
• [BUGFIX] Reset elision: do not use zero as special stream ID value, for zero is a valid stream ID in IETF QUIC.
• [API] Add optional on_conncloseframe_received() callback.
• Use zero error code in RESET stream sent in response to STOP_SENDING.

Fix migration corner cases and stream unit test

• [BUGFIX] Migration corner cases: drop or pad over path challenge and response frames when necessary.
• Fix stream unit test.

Handle packet reordering; add parameter to get_ssl_ctx() callback

• [OPTIMIZATION] Adjust packet reordering threshold when spurious losses are detected.
• [API] Pass pointer to local sockaddr to ea_get_ssl_ctx() callback.

Option to delay on_close; new on_reset callback

• [API, FEATURE] Add es_delay_onclose option to delay on_close until all data is ACKed. Use new function lsquic_stream_has_unacked_data() to learn whether peer acknowledged all data written to stream.
• [API] Add optional on_reset() stream callback to get notifications when RESET or STOP_SENDING frames are received.
• [BUGFIX] On STOP_SENDING, make conn tickable is writeable, not readable.

Delayed ACKs; limit receive history

• [FEATURE] Improve Delayed ACKs extension and turn it on by default.
• Limit receive history to a finite amount of memory.

Bug fixes: CC, CIDs, memory leak

• [BUGFIX] Check whether ECN counts are set in ACK struct before using them.
• [BUGFIX] Calculate TLP timer correctly when only one packet is in flight.
• [BUGFIX] Min RTO delay is 200 milliseconds, not 1 second.
• [BUGFIX] Memory leak in QPACK decoder handler: discard hset when necessary.
• Allow retired and drained CIDs to be reused after a timeout.

Bug fixes

• [BUGFIX] min RTO delay is 200 ms , not 1 second.
• [BUGFIX] calculate TLP timer correctly when only one packet is in flight.
• [BUGFIX] discard CRYPTO frames from lower levels after connection promotion.
• [BUGFIX] cancel path response if path could not be initialized.
• [BUGFIX] if push promise fails, do not invoke hset destructor.

Bug fixes: client BBR, memory leak

• [BUGFIX] Get rough RTT estimate on receipt of Handshake packet. This prevents BBR on the client from miscalculating pacing rate, slowing down sending of ACK packets.
• [BUGFIX] Packets sent during handshake are app-limited.
• [BUGFIX] Bandwidth sampler starts in app-limited mode.
• [BUGFIX] Memory leak: free QPACK handler context in stream dtor.
• Logging improvements.

Migration and coalescing bug fixes

• [BUGFIX] Allow peer to migrate when its SCID is zero-length.
• [BUGFIX] PADDING size calculation: only one Short packet can be coalesced. (This should have been part of the fix in 2.24.1).
• Abort connect if received NEW_CONNECTION_ID but current DCID is zero-length.
• Improve log messages

SSL_CTX for client; bug fixes

• [API] Allow use of ea_get_ssl_ctx() on the client (optional). PR #186.
• [BUGFIX] Expand datagram with ack-eliciting Initial to 1200 bytes after connection promotion.
• [BUGFIX] Discard CRYPTO frames from lower encryption levels after connection promotion.
• [BUGFIX] Cancel path response if path could not be initialized.