...G...PS. [ZBX-8391] stronger command-line parameter validation, revised help and version messages, revised man-pages for Zabbix server, proxy, agent, sender and get utilities

Before this change:
   - an option could be specified multiple times on command-line,
   - unnecessary arguments (unrelated to options) could be specified on command-line,
   - it was not clearly described which options are mutually exclusive.
After this change:
   - using the same option several times is an error,
   - using parameters which are not option values is an error,
   - using mutually exclusive options is an error.
   - man-pages revised and their formatting improved.
   - help and version messages displayed with '-h' and '-V' options are closer to GNU recommendations