crocket 0.2.0

One Config for everything, configurable from the environment. Breaking: settings
moved, so code that sets them needs the new names.

Changed

• LaunchOptions is gone; Config holds every setting, in groups: server
  (listen, host, port, workers, event_loops, tls_cert, tls_key, http2,
  h2_prior_knowledge), limits (max_body_bytes, max_body_memory, max_in_flight,
  max_header_bytes, max_header_count, max_connections, max_connections_per_ip,
  http2_max_streams, etag_max_bytes), timeouts (request, drain) and proxy
  (trusted, header, allowed_hosts), plus profile, debug_routes, json, log
  and adaptive_placement. Having two structs made it unclear where a setting lived
  and which of them the environment reached.
• launch() serves on cfg.server; launch({...}) takes ServerOverrides, which
  overrides only the server fields you name: .launch({.listen = "8080"}).
  listen accepts "8080", ":8080", "host:8080" and "[::1]:8080".
• Config::from_env() reads every CROCKET_* setting, not just CROCKET_PROFILE,
  with strict parsing: a bad value throws std::invalid_argument naming the variable
  (CROCKET_PORT=tcp://10.43.0.12:8000 is rejected instead of misread).
  Config::from_env(base) layers the profile and environment over your own defaults.
  Precedence: defaults < base < profile < environment < code < launch({...}).
• CROCKET_REQUEST_TIMEOUT accepts units (500ms, 30s, 2m); a bare number is still
  seconds. CROCKET_DEBUG_ROUTES is a boolean now: 0/false turns it off.
• examples/serve.cpp, grpc.cpp and hello.cpp use Config::from_env() and
  launch() instead of mapping variables by hand.

Migrating from 0.1

0.1	0.2
cfg.request_timeout, cfg.drain_timeout	cfg.timeouts.request, cfg.timeouts.drain
cfg.max_body_bytes, max_in_flight, max_body_memory, etag_max_bytes	cfg.limits.*
cfg.trusted_proxies, proxy_header, allowed_hosts	cfg.proxy.trusted, .header, .allowed_hosts
LaunchOptions{.max_connections = ...} and the other limits	cfg.limits.*
.launch({.host = ..., .port = ..., .tls_cert = ...})	unchanged, or cfg.server.* and .launch()
Hand-written getenv("CROCKET_...")	Config::from_env()