loko 0.2.0

The first release of loko as a services library. It is version 0.2.0 because the loko name on crates.io carries an
unrelated 0.1.0 from 2022 (task scripting), by the same owner.

Added

• loko-clock: the Clock service (now, now_ms, sleep), TestClock, StdClock, TokioClock (feature
  tokio), JsClock (feature js), and OffsetClock, a clock ahead or behind another.
• loko-random: the Random service, a source of rand_core generators (rng(), drawn from with no locks);
  SeededRandom (SeededRng, SplitMix64, for tests), OsRandom (feature getrandom, OsRng), JsRandom (feature
  js, JsRng), and Random for a Mutex around any seedable rand_core generator. The OS and JavaScript generators
  are CryptoRng, so code that makes secrets can ask for Random<Rng: CryptoRng>.
• loko-env: the Env service (var, vars), SystemEnv, and MapEnv.
• loko-console: the Console service (print_line, print_error_line), StdConsole, TestConsole, and
  JsConsole (feature js).
• loko-store: the Store service (objects by URI, with put-if-absent, multipart uploads, and prefix listing),
  MemoryStore, an error type, and the wrappers CountingStore (counts calls), ReadOnlyStore (refuses writes), and
  PrefixedStore (passes on only URIs under a prefix).
• loko-object-store: a Store over an object_store client, from a client or a URL.
• The service crates depend on nothing but rand_core (for loko-random); the macros are needed only to define
  new services.
• loko-macros: #[service], which adds a HasX trait to a service trait X and makes every HasX an X, and
  #[loko::bundle], which makes a struct each service its fields provide, and #[wraps], which makes a wrapper
  that replaces some of a service's methods and forwards the rest.
• loko: the services under one crate (loko::clock, …, loko::store with feature store), the platforms
  TestPlatform, StdPlatform, TokioPlatform, and JsPlatform, and a prelude.