Added new archive numbering mode

Implemented a new archive numbering mode, called DateAndSequence. As the name suggests, this is a combination of "Date" and "Sequence" archive numbering mode. 

Now it's possible to use a combination of ArchiveEvery = Day, ArchiveAboveSize and MaxArchiveFiles.

Logfiles are archived in the following format when ArchiveDateFormat is set to yyyy-MM-dd:

MyLog.2014-11-25.0.log
MyLog.2014-11-25.1.log
MyLog.2014-11-26.0.log
MyLog.2014-11-26.1.log