Implement QL loss bits extension, bug fixes

• [FEATURE] Implement the QL extension (offered by default).
• [BUGFIX] Abort when encountering unexpected HTTP/3 frames.
• [BUGFIX] Acknowledge (QPACK) HTTP/3 trailers correctly.
• [DEBUG] Turn on debug message for next advisory tick.

Bugfix release

• [BUGFIX] Using HTTP/3 to HTTP/1.x converter.
• [BUGFIX] Truncate log messages instead of throwing them away.

Bugfix release

• [BUGFIX] High priority buffered packet queue length.
• [BUGFIX] Rain time calculation: max_ack_delay is in milliseconds.

Bugfix release

• [BUGFIX] Close DATA frames with empty payload correctly.

Bugfix release

• [BUGFIX] SCID!=ODCID rule applies to Retry packets, not regular packets.
• [BUGFIX] Zero-RTT: BoringSSL no longer flips read/write secrets.
• [BUGFIX] Truncate ACK frame rather instead of aborting IETF connection.
• [BUGFIX] Client: don't send duplicate reset tokens.
• [BUGFIX] Remove invalid assertion in H3 framing code.
• Silence a warning in send ctl by restructuring switch() statement.

Bug fixes and improvements from early Interop

• [BUGFIX] set retry token on all resubmitted packets.
• Event log: log sent packet flags. In particular, this allows one to see whether token was sent.
• Don't migrate client if es_allow_migration is false.

Support Internet Draft 24

Internet Draft 23 is also supported, as well as Q039, Q043, and Q046

Bug fixes

• [BUGFIX] argument order to gQUIC client constructor. Regression introduced in 2.5.0.
• [BUGFIX] split buffered packet error recovery: destroy the correct packet.

Bug fixes, optimizations

• [BUGFIX] Fix double-free when emptying a packet number space.
• [BUGFIX] http_server: fix md5sum handler: handle EOF correctly.
• [BUGFIX] Use random values in bits 4 and 5 of the first byte of verneg packets (regression introduced in 2.5.0).
• [OPTIMIZATION] Don't compile in expensive attq checks by default.
• [OPTIMIZATION] http_server: compile regexes only once.

API change, optimizations, bug fixes

• [API] lsquic_engine_connect() can now be passed QUIC version to use.
• [OPTIMIZATION] Queue opportunistic ACKs if there is data to be sent.
• [BUGFIX] Don't evict streams from priority iterator if there is only one queue.
• [OPTIMIZATION, BUGFIX] Several other optimizations and bug fixes.
• Use ls-qpack v0.10.7.