post: url parameter was not used

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
post: support both application/x-www-form-urlencoded and application/json style webhooks.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
post: Support HTTP Digest authentication.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>