v1.0.0.dev3

• added a background thread to process the transactions queue every 60 seconds (configurable) (#68)
• adapted trace context for SQL traces to new API (#77)
• ensured that transaction data is also passed through processors (#84)
• added uninstrument function to reverse instrumentation,
  and exposed both instrument and uninstrument as public API in the elasticapm namespace (#90)
• added normalization of HTTP status codes into classes for the transaction.result field. A HTTP status of 200
  will be turned into HTTP 2xx. The unchanged status code is still available in context.response.status_code.
  (#85)