New features (large payload truncation, items per minute and log level settings) and fixes

resolve #81: Truncate large payloads to ensure we don't drop them
resolve #84: Add items per minute config option
resolve #107: logging an exception does not include extra data into a payload
resolve #109: when an NSException is reported with an auxiliary message it is not reported as a trace object
resolve #87: Add log level config option
resolve #111: Add telemetry example
resolve #113: Eliminate payload batch sending - send one payload at a time