Separate CMakeLists.txt for etc/initsystem.

Refs #6491
Docs: fix typos in chapter 8.

Signed-off-by: Michael Friedrich <michael.friedrich@netways.de>
Merge branch 'feature/separate-CMakeLists-6491' into next

fixes #6491
Add (s)smtp_mail_from option to smtp and ssmtp commands.

Refs #6487
Add http_expect_body_regex and http_ignore_body to command-plugins.conf.

Refs #6487
Add "ssl" CheckCommand

Refs #6487
Improve snmp CheckCommand, add snmpv3 CheckCommand.

Refs #6487
Add CheckCommand "dns"

Refs #6487
plugin command dns: small naming fixes

refs #6487