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
Fixed UDP broadcasting for UdpNetworkSender
Added tests for UDP broadcast
Fixed bug whereby collection we were iterating over was modified during
iteration.
Merge pull request #439 from dmitriyett/master

Fix for UDP broadcast
Merge pull request #442 from tsconn23/master

BUG FIX: Modification to LogEventInfo.Properties While Iterating
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
added enum value DateAndSequence
implemented new archive numbering mode DateAndSequentialArchive
implemented support for hidden assemblies
Merge pull request #448 from reedyrm/master

Added unit test to identify work around when using colons within when layout renderers
added test HiddenAssemblyTest inside of CallSiteTests.cs
added new assert method: AssertFileSize
added unit test for archivenumbering-mode DateAndSequence