logging: enhanced debug logging across all core modifiers

[admtnnr]

All the core modifiers, filters, and verifiers should have increased debug log output (log.Debugf) so it's easier to trace which modifiers were called and which values were modified.

Individual Modifiers

• [ ] auth.Filter
• [ ] body.Modifier
• [ ] cookie.Modifier
• [ ] fifo.Group
• [ ] header.ForwardedModifier
• [ ] header.FramingModifier
• [ ] header.BlacklistModifier
• [ ] header.Filter
• [ ] header.Modifier
• [ ] header.Verifier
• [ ] header.HopByHopModifier
• [ ] header.ViaModifier
• [ ] ipauth.Modifier
• [ ] martianhttp.Modifier
• [ ] martianurl.Modifier
• [ ] martianurl.Filter
• [ ] martianurl.Verifier
• [ ] method.Verifier
• [ ] pingback.Verifier
• [ ] priority.Group
• [ ] proxyauth.Modifier
• [ ] querystring.Modfier
• [ ] querystring.Filter
• [ ] querystring.Verifier
• [ ] status.Modifier
• [ ] status.Verifier