Ban time incr

New feature "automatically exponential increasing ban time".
WARNING: by first start the server upgrades sqlite database (table "bans" will recreated with another schema);
Option "bantime.increment" in jail.conf allows to use database for searching of previously banned ip's to increase a default ban time using special formula, by default each next ban increase banTime * 1, 2, 4, 8, 16, 32...
see "jail.conf" for some other options of "bantime.___";
additional we can configure a little randomization of ban time, to prevent "clever" botnets calculate exact time IP can be unbanned.

Sorry @sebres. I now realise that info about _Fail2Ban_'s preferred documentation format isn't really clear anywhere (need to update _DEVELOP_ file).
The preferred style in the _numpy_[1] format.  _fail2ban.server.actions_[2] is probably a good example.

[1]: https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt
[2]: https://github.com/fail2ban/fail2ban/blob/master/fail2ban/server/actions.py