Patch by F.Chaix : add two "new" log appender methods : split and roll

Patch by F.Chaix : add two "new" log appender methods : split and roll
split will create new files when a specified size is reached
roll will overwrite the file when this size is reached
example syntax is : --log=root.appender:splitfile:10000:myfilename_%.txt

The % is a wildcard that will be replaced by the number of the file. If no % is present, it will be at the end