Algernon 1.15.3

• Support Go 1.21 and drop support for Go 1.19 (thanks @stefanb).
• Enable QUIC support for non-x86_64 macOS, like M1 and M2.
• Fix an issue when building with -tags=trace, for benchmarking.
• Update the welcome.sh script with regard to ulimit and sysctl kern.maxfiles detection.
• Improve the --help output and the REPL help.
• Let the style for the "Welcome" page be slightly more welcoming.
• Improve the Makefile.
• Some minor changes to the code.
• Adjust the example server config.
• Update dependencies.