Make ExceptionLayoutRenderer more extensible

Right now there's no easy way to tweak how a particular layout token (i.e. Message or Data) is rendered by extending ExceptionLayoutRenderer, because the Append... methods are private static
- Convert Append... methods from private static to protected virtual
- Change ParseMethodNameFromStackTrace from private to protected
Fix compile issues/warnings
Merge pull request #430 from SurajGupta/master

Make ExceptionLayoutRenderer more extensible
Implement Flush in LogReceiverWebServiceTarget

Do ensure events aren't lost when app is terminated
closes #429
Change GetCandidateFileNames() to also yield appname.exe.nlog when config file is appname.vshost.exe.config
Merge pull request #443 from Xharze/LogReceiverWebServiceTargetFlush

Implement Flush in LogReceiverWebServiceTarget
Merge pull request #447 from jltrem/vshost-config

Change GetCandidateFileNames() to also yield appname.exe.nlog when confi...
Added unit test to identify work around when using colons within when layout renderers
Merge pull request #448 from reedyrm/master

Added unit test to identify work around when using colons within when layout renderers