Limit header sets, spec compliance fixes

• [API, IMPROVEMENT] Limit number of buffered header sets to cap memory use.
• [FIX] Client: return correct error on bad transport parameters (issue #616).
• [FIX] Don't abort on receipt of STOP_SENDING in Ready state (issue #658).
• [FIX] Fix FIU linking.

Fix content-length handling plus latest ls-qpack

• [FIX] Reject HTTP messages with multiple conflicting content-length
  fields.
• [FIX] Use ls-qpack v2.6.5 to pick up a fix for a latent use-after-free.
• [IMPROVEMENT] Handle unexpected stream readv/writev args correctly.
• [DOCS] Update docs about the now-defunct push promises.

Bytes-scheduled underflow and other fixes

• [FIX] Send controller: bytes-scheduled underflow (issue #652).
• [FIX] Enforce stream limit in RST_STREAM (issue #654).
• [FIX] Reject invalid Content-Length syntax.
• [IMPROVEMENT] Top-level cmake ASAN options.

Deprecate gQUIC; various fixes

• [API] Deprecate all gQUIC versions.
• [FIX] http1x: check size of Cookie: header.
• [FIX] Add checks to gQUIC client session resume code.
• [FIX] 32-bit parser bounds checks.
• [FIX] Use ls-qpack v2.6.3 to pick up a bunch of fixes.
• [DOCS] FAQ: example programs do work with google.com etc.

Fixes for priority handling and preferred address transport params

• [FIX] Only ignore Priority: header after PRIORITY_UPDATE and in
  client mode.
• [FIX] Transport params: reject partial preferred address families.
• [IMPROVEMENT] PRIORITY_UPDATE frame handling.

Header validation, recvmmsg, edge case fixes

• [FIX] Content-length check in QPACK decoder handler.
• [FIX] HTTP/1.x module: stricter validation for field names and values.
• [FIX] Sample tools: fix recvmmsg receive batching (issue #434).
• [FIX] crypto object ownership on promotion failure.
• [IMPROVEMENT] Use ls-hpack v2.3.5.

Better hset handling and refactorings

• [IMPROVEMENT, API] Refactor: drop mini-conn promotion shortcut.
• [IMPROVEMENT, API] Improve multiple incoming header set handling.
• Remove unused push promise support. API stays unchanged for now.

Use EAGAIN for pending headers

Release 4.6.4

- [IMPROVEMENT] Use EAGAIN for pending headers (follow up to 4.6.3)

Two small fixes for edge cases

• [FIX] Reject overlapping header sends, making code safer.
• [FIX] Follow spec: max datagram size of zero disables datagrams.
• [IMPROVEMENT] Include statement for vc_compat.h to use quotes.

Fix ACK generation edge case; better hashing; other improvements

�- [FIX] Prevent ACK frame generation overflow (unlikely).

• [IMPROVEMENT] Update README BoringSSL version to current date tag.
• [IMPROVEMENT] Address unterminated-string-initialization warnings.
• [IMPROVEMENT] Cast 1 to uint64_t to future-proof code.
• [IMPROVEMENT] Use better random number for hashes.
• [IMPROVEMENT] Inconsistent capitalization fo ws2tcpip.h.