Add option fir Unix/GNU CLI standard

Created by: suvorov21

Add optional support of Unix/GNu CLI interface. That mostly inherits from standard POSIX, but with the extension for long options.

Since the standard is widely used by developers I expect such an option will enrich the package. E.g. GNU getopt/optatrg works exactly like that.

E.g.: ./app.exe -abc == ./app.exe -a -b -c ./app.exe -i../test.dat == ./app.exe -i ../test.dat ./app.exe --input=../test.dat == ./app.exe --input ../test.dat

The main changes:

1. Check the option upon adding to CliParser with GNU standards
2. Completely independent parser function in case GNU option is on.

So far, only implementation is done, w/o documentation and examples. If you found the PR positive, I can easily add examples before merging.