Stable release

Changes

• SIP TLS support, using Rust and Tokio-rustls
• If no cert.pem or key.pem files are found, we automatically create them for you in the current working directory for a seemless start up experience
• -N option to revert to old C way with select() for TCP and UDP
• TCP, UDP now all powered by Rust and Tokio
• We now support TLS configuration loaded from config using confy
• If a cert or key file is not found using -t or -k options, SentryPeer will
  ask you if you'd like to create them - we use the very nice rcgen for this
• New -z, -tand-k` options for SIP TLS support
• Command Line Interface (CLI) now powered by Rust using clap-rs
• Environment variables SENTRYPEER_CERT, SENTRYPEER_KEY and SENTRYPEER_TLS_LISTEN_ADDRESS
• We now look for cargo and rustc, as we are porting parts of SentryPeer to Rust. New features will be written in Rust
• SIP TLS support and other Rust-powered features will not be built if Rust is not detected.
• make check now runs Rust tests
• make clean cleans up Rust builds
• --enable-debug argument added to ./configure to enable debug mode for Rust code. Default is --release
• --enable-silent-rules and make V=1 honoured in Rust code build
• --disable-rust argument added to ./configure so you can disable Rust code build
• CMakeLists.txt updated to build Rust code and run all tests. We're using https://github.com/corrosion-rs/corrosion for this
• README.md updated to reflect the new Rust code build options, and CMake build instructions that now also
  include Rust code and running our tests
• Show CPPFLAGS and LDFLAGS in configure status summary as needed to do macOS builds if on arm64