v1.0.0 — first stable release

First stable release. The public surface — the span & metric emitters, the
Contracts\* interfaces, config keys, and the FailSafe guarantees — is now
covered by Semantic Versioning, and the 1.x line commits to backward
compatibility. Functionally this promotes the 0.4.x line to stable; there are no
behavioural changes beyond the fix below, which was staged as 0.4.1 but never
tagged and is rolled up here.

Fixed

• Redis instrumentation no longer tries to open the client/options/cluster
  config keys as connections. When instrument.redis is on, retro-fitting
  already-resolved connections enumerated every key under database.redis and
  skipped only options, so a client key (the phpredis/predis selector, present
  in every default Laravel config) threw "Redis connection [client] not configured"
  on every request. It was FailSafe-guarded, so no request broke, but it flooded
  the log. All reserved keys (client, options, cluster) are now skipped. (#4)