Release 1.3.0

New stuff:

• Add dumdohd, reflect DNS-over-HTTPS using nghttp2 example server
• Add -Q <num> to set listen backlog
• Dockerfile
• Add clang-format and format code

Bugfixes and tweaks:

• Update README about compiling environment
• Fix #20: Flush stdout on stats
• dumdohd: Remove deprecated OpenSSL functions
• dumdumd: Ignore SIGPIPE, can happen during BIO_write()

404fd43 listen backlog
888676b Make listen backlog configurable
28a7a29 Split Dockerfile to build and runtime phases to cut down image size
097686f Add dumdohd to .gitignore
9f01560 Dockerfile
196fcc1 OpenSSL 3.0, SIGPIPE
98e962a DoH
c2c8bf3 DoH random goaway
a738383 DoH
5683124 Dockerfile
b33675c Flush stdout
4acb0bd README
b8f3e4d Fix changelog