Release nghttp3 v1.6.0 · ngtcp2/nghttp3

What's Changed

Change clang-format options by @tatsuhiro-t in #249
Fix cmake export by @talregev in #248
Fix include export by @talregev in #250
Fix ARM64 __popcnt intrinsics by @fcharlie in #252
Refactor qpack reserve_buf by @tatsuhiro-t in #253
Fix potential overflow by @tatsuhiro-t in #254
nghttp3_map: Port ngtcp2 changes by @tatsuhiro-t in #255
Optimize nghttp3_read_varint by @tatsuhiro-t in #256
Consistent macro comments by @tatsuhiro-t in #258
clang-format files under fuzz by @tatsuhiro-t in #259
ispow2: Better fallback implementation by @tatsuhiro-t in #260
Refactor http on header by @tatsuhiro-t in #261
Simplify http_request_on_header and http_response_on_header by @tatsuhiro-t in #262
qpack: Switch on opcode by @tatsuhiro-t in #263
Do huffman encoding only when the reduction is more than 25% by @tatsuhiro-t in #264
Optimize nghttp3_check_header_value by @tatsuhiro-t in #265
Revert "Optimize nghttp3_check_header_value" by @tatsuhiro-t in #266
cmake: Remove trailing spaces by @tatsuhiro-t in #268
Optimize nghttp3_check_header_value by @tatsuhiro-t in #267

Full Changelog: v1.5.0...v1.6.0