Configuration for YARD

http://yardoc.org/
http://www.rubydoc.info/github/yast/yast-ftp-server
Document FtpServerClass a bit.

Made YARD see the attributes of FtpServer.
Documented the *_SETTINGS attributes.
Removed commented out code and excess empty lines.
Removed unused methods Overview, AbortFunction.
changelog
Using different defaults about logging for vs/pure-ftpd (bnc#888287)
added testcase
setting xferlog_enable instead of syslog_enable
Version bump; Changelog