Spf4j 8.4.4 release

Some of the notable features new in 8.4.4:

ExecutionContext + stack sampling => ssdump3 (aka labeled stack samples). This allows you to collect samples for execution contexts. This should reduce the sampling overhead, and should improve the relevance of the samples. This functionality is now in Beta, and I still have to document it, but one can get started at: SsdumpTest.testTracingDumpExecContexts...

The slf4j test module is maturing nicely:
http://www.spf4j.org/spf4j-slf4j-test/index.html

spf4j now contains a java.util.logging -> slf4j redirector which is designed to easily replace jul-to-slf4j with that unlike the official one, is more complete and faster.

Fixed some issues with JdbcSemaphore.

Migrated the entire code base to TimeSource allowing to easily switch between System.currentTimeMillis, System.nanotime, or other timers...

The new RetryPolicy api is now in BETA and maturing, and allows for complex retry handling which was not possible before. The existing retry api in Callables is now deprecated.

Spf4j UI now supports ssdump3 (labeled dumps), easier to use the graph or stack view, and faster.