0.16.0

Changes:

• Revise config value API
  • Deprecate all individual members of actor_system_config
  • Add get_or(name, default) API for accessing settings
• Implement CE-0002
• Add experimental streaming feature
• Add C++17-compatible string_view class
• Remove legacy ASIO-based multiplexer
• Add IP address and subnet classes for v4 and v6
• Add URI abstraction according to RFC 3986
• Improve testing DSLs for deterministic testing
• Fix the "quiet" log level and output to uncolored terminals