org.apache.logging.log4j.core.appender.AsyncAppender.getThreadQueueSize()
to help synch tests in applications.

mongo tests intermittenly fail with an "Operation not permitted"
IOException when trying to execute the mongod extracted by
de.flapdoodle.embed.process; this seems to be related to surefire
running tests in parallel. Work around that here by forcing serial
execution of the mongo tests.

This closes #201

When emptyReplacement length is less than 10 but large enough for
the current paramers, the ReusableParameterizedMessage would
retain references to the most recently logged parameters.

This closes #200

Combine codepaths for initial and terminal fragments.
Add changelog entry.

This closes #188

session logger failed (Closes #198).

Regression introduced here, removing StackLocator.SECURITY_MANAGER
initialization: 55b9fd20

Removed a few  unnecessary parameters and operations.

ExtendedThrowablePatternConverter no longer constructs a String
of the full stack trace, instead appending to the layout
StringBuilder.

This does not provide any benefit for
ExtendedThrowablePatternConverter.

Updated Benchmarks:

Benchmark                                                Mode  Cnt       Score       Error  Units
FileAppenderThrowableBenchmark.julFile                  thrpt    3   42411.701 ±  9740.338  ops/s
FileAppenderThrowableBenchmark.log4j1                   thrpt    3   58608.053 ±  9127.229  ops/s
FileAppenderThrowableBenchmark.log4j2ExtendedThrowable  thrpt    3   15443.610 ±  3942.549  ops/s
FileAppenderThrowableBenchmark.log4j2SimpleThrowable    thrpt    3  114443.966 ± 29211.657  ops/s
FileAppenderThrowableBenchmark.logbackFile              thrpt    3  135646.780 ± 16794.353  ops/s

Initial results (re-ordered fastest to slowest):

Benchmark                                                Mode  Cnt       Score       Error  Units
FileAppenderThrowableBenchmark.logbackFile              thrpt    3  135260.838 ± 15790.010  ops/s
FileAppenderThrowableBenchmark.log4j2SimpleThrowable    thrpt    3   87385.712 ±  8082.803  ops/s
FileAppenderThrowableBenchmark.log4j1                   thrpt    3   60359.485 ± 10122.858  ops/s
FileAppenderThrowableBenchmark.julFile                  thrpt    3   52134.431 ±  1302.365  ops/s
FileAppenderThrowableBenchmark.log4j2ExtendedThrowable  thrpt    3   15348.378 ±  1301.501  ops/s

interrupted thread.

interrupted thread.