Feature request: allow custom JSON replacer function

Allow custom JSON replacer function to be passed in via options, which will allow us to sanitize sensitive data from the logs (passwords, cc info, etc), helpful if objects passed into meta. Pull request incoming.

Start by reviewing how logger options are accepted and how objects passed through meta are serialized. Define the replacer option's expected behavior for sensitive values such as passwords and credit-card information, then verify that sanitized metadata is emitted in logs without changing behavior when no replacer is provided.

Written by the indexing model from the issue text.