Tabkit

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* Cumulative sum.
* Cumulative count.
* Fix group concat delimeter argument.

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* Writer substitutes \n, \t with \v

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* Group concat.

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* tgrp_awk - perform group operation.

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* Change SyslogStream to LogStream. Use LogStream(logging.handlers.SysLogHandler(), ...) to achieve the same.
(Reason: syslog.syslog() uses libc syslog() which limits message to 2048 chars under FreeBSD)

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* Fix boolean values parsing