Bugfix/access logger corner cases

[nicmunroe]

• Firms up tracking when requests start and end, and at a higher granularity (nanoseconds).
• Also tracks when the last payload chunk arrives (allows you to diagnose when slow response times are due to callers slowly trickling in their payloads).
• Removes span name from access logger output defaults - callers shouldn't be sending this and it's a waste of characters in the log message.
• Handles corner cases so that access logging is always performed, e.g. when the caller drops connection before the response has been sent.

[codecov-io]

Codecov Report

Merging #93 into master will increase coverage by 0.07%.
The diff coverage is 97.95%.

@@             Coverage Diff              @@
##             master      #93      +/-   ##
============================================
+ Coverage      91.3%   91.37%   +0.07%     
- Complexity     2091     2109      +18     
============================================
  Files           148      148              
  Lines          6070     6109      +39     
  Branches        794      799       +5     
============================================
+ Hits           5542     5582      +40     
+ Misses          356      355       -1     
  Partials        172      172

Impacted Files	Coverage Δ	Complexity Δ
...server/channelpipeline/HttpChannelInitializer.java	100% <ø> (ø)	30 <0> (ø)	⬇️
...oste/metrics/codahale/CodahaleMetricsListener.java	100% <100%> (ø)	40 <0> (ø)	⬇️
...a/com/nike/riposte/server/http/ResponseSender.java	73.51% <100%> (+0.12%)	61 <1> (+1)	⬆️
...ke/riposte/server/handler/AccessLogEndHandler.java	90% <100%> (ø)	11 <0> (ø)	⬇️
.../com/nike/riposte/server/logging/AccessLogger.java	96.29% <100%> (+1.44%)	48 <0> (+2)	⬆️
.../riposte/server/handler/AccessLogStartHandler.java	100% <100%> (ø)	9 <2> (+3)	⬆️
...erver/handler/ChannelPipelineFinalizerHandler.java	100% <100%> (ø)	46 <0> (+3)	⬆️
.../nike/riposte/server/http/HttpProcessingState.java	99.01% <94.73%> (+1.42%)	45 <9> (+10)	⬆️
...mpipeline/DownstreamIdleChannelTimeoutHandler.java	85% <0%> (-5%)	4% <0%> (-1%)
...ient/asynchttp/netty/StreamingAsyncHttpClient.java	75.52% <0%> (-0.24%)	46% <0%> (ø)
... and 3 more

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