LOGBACK-266 - allow max window size to be overriden
LOGBACK-266 - increase max window size of FixedWindowRollingPolicy to 20.  12 is too restrictive, and the users have voted for it to be increased
Merge pull request #110 from diroussel/LOGBACK-266

Fix for LOGBACK-266 - FixedWindowRollingPolicy MAX_WINDOW_SIZE too small