feature: added support for command-line arguments parsing

* Adding support for command-line arguments parsing
* Adding support for multiple directories to the search paths for Lua libraries
* Using Getopt::Long instead of Getopt::Std
* Adding a new test scaffold
* Adding support for specifying the nginx path (this option might be removed in the future)
I don't like this Perl module name. It's usually against the Perl module naming convention. How about `Test::RestyCLI`? The original `Test::ktap` module name in the `ktap` project was like that just because Jovi hates capitalizing his `ktap` name.