Add keyword argument `raise_send_errors` to the `capture` method (and subsequent `send` methods)
of the base `Client` as well as to the `emit` method of various `SentryHandlers`.
This indicates whether the client must handle or raise any exceptions encountered while sending to Sentry.
* The default argument (False) matches the current behaviour in which the client/logging handler handles the error.
* Setting this argument to True allows for the calling application to handle the exception and
  thus determine its own retry and backoff strategies.