Fix #54 - adding a configuration to log full stack trace in error.stack

[jlopezinc]

Include full exception stack trace

Only supported on logback

You can configure the logging extension to include in error.stack the full stack trace just like the downstream library does.
This includes the caused by chain.

As an example, this snippet:

Exception inner2 = new IllegalAccessException("test caused by 2");
Exception inner1 = new RuntimeException("test caused by 1", inner2);
LOGGER.error("failed for test!", new RuntimeException("test exception", inner1));

Will set the error.stack as

java.lang.RuntimeException: test exception
    at (regular stacktrace)
    at ...
Caused by: java.lang.RuntimeException: test caused by 1
	... 49 common frames omitted
Caused by: java.lang.IllegalAccessException: test caused by 2
	... 49 common frames omitted

Default is false for retro-compatibility.

This setting can be enabled via environment variable (NEW_RELIC_LOG_EXTENSION_INCLUDE_FULL_ERROR_STACK=true) or system variable (-Dnewrelic.log_extension.include_full_error_stack=true).

Be aware that enabling this setting will use the downstream library's stacktrace generation, not taking in consideration
the value of Exception Stack Trace Size.

[CLAassistant]

All committers have signed the CLA.

[trico-tillster]

Looks good

[jtduffy]

Closing - fixed by #82