Added longjohn dependency to package.json
Added 2-way SSL/TLS client certificate authorization; revised HMAC authorization; corrected error audit-logging bug from cyclical error instance being logged; added "503/Service Unavailable" response to proxy_client request error event; added content-type to error responses; revised error response body texts; removed longjohn dependency.
Added round-robin load-balancing for multiple hostname, path routes.
Removed load-balancing debug output.
Merge pull request #8 from JohnWMay/master

Added longjohn dependency to package.json