stratify 0.3.1

Added

• EnvSource::with_keys and ConfigBuilder::env_keys, capturing exactly the
  environment variables you name rather than everything matching a prefix.

  Some settings are named by convention rather than by application: RUST_LOG
  is read by tracing-subscriber, AZURE_STORAGE_ACCOUNT is what Azure
  injects. No prefix selects those and nothing else, and an empty prefix
  captures the whole environment — PATH and every other process's secrets
  along with it, which then sits in the merged configuration waiting to be
  logged.

  Names match case-insensitively and appear lowercased, so RUST_LOG is read as
  rust_log. The separator still applies.