* logging: Implement dial timeout for net writer (fix#4083)
* Limit how often redials are attempted
This should cause dial blocking to occur only once every 10 seconds at most, but it also means the logger connection might be down for up to 10 seconds after it comes back online; oh well. We shouldn't block for DialTimeout at every single log emission.
* Clarify offline behavior
* httpcaddyfile: Begin implementing log directive, and debug mode
For now, debug mode just sets the log level for all logs to DEBUG
(unless a level is specified explicitly).
* httpcaddyfile: Finish 'log' directive
Also rename StringEncoder -> SingleFieldEncoder
* Fix minor bug in replacer (when vals are empty)
