v1.7.0-alpha.20

• #139 Refactor for using as a library. Move signal monitor outside of shadowsocks library.
• #141 Build with Rust 2018.
• Update dependencies. --feature miscreant is now can be built with stable.
• Support no_delay: bool in config.
• [Breaking] Replace enable_udp with mode, possible values are: tcp_and_udp, tcp_only, udp_only.
• #85 Support ss-manager reports.