Merge branch 'knotc-improvements' into 'master'

knotc improvements

Improved `knotc` commands + unified and improved help, man and documentation.

- `reload` and `zonestatus` now take arguments and can be called for particular zones
- fixed logging of incoming command (was printing only the last argument)
- fixed use of RCU in remote command processing.
- updated help (`knotc -h`), man page and doxygen documentation
- warning when no arguments are supplied to `refresh -f` and `signzone` (they require at least one argument)
- warning when arguments are passed to `stop` and `checkconf` (they take no arguments)

Fixes #308

See merge request !309