feat: optionally include buffer in send/error events.

With this change, the user may specify a verboseEvents boolean option when creating a logger. If true, the logger will include the buffer of messages that was sent (or attempted to be sent) when emitting send and error events, in the buffer member of the send event and the meta.buffer member of the error event. This enables users to correctly identify the messages that were transmitted for metrics in case of success, and to implement higher-level retry behaviors in case of errors.

lib/logger.js: Add support for verboseEvents option. (send): When emitting send and error events, include the message buffer involved when verboseEvents is true. In case of partial success, each error event will include a buffer containing only the specific line that failed; and the corresponding send event will include a buffer containing only those lines that were sent successfully.
test/common/create-options.js:
test/logger-errors.js:
test/logger-instantiation.js:
test/logger-log.js: Add tests for verboseEvents.
README.md:
types.d.ts: Update readme and type definitions.

Fixes: #60

logdna / logger-node

feat: optionally include buffer in send/error events. #61