New library: argparse, for parsing CLI arguments

[Andrey Zherikov]

Hi everyone,

I'm happy to announce that I've published a CLI argument parsing 
library - [argparse](https://code.dlang.org/packages/argparse). 
It's been around for some time already so please take a look and 
provide your feedback if you haven't done so.

The reasoning to create one more CLI parsing library is that the 
existing libraries do not provide enough flexibility in parsing 
that I'm looking for and/or they depend on other libraries. As a 
result `argparse` supports wide variety of data types including 
enums, callbacks and arrays as well as a fully customized 
argument parsing. It also doesn't depend on anything besides the 
standard library.

Since it's in active development (activeness depends on my 
availability of course), I have few things to do before making 
the first major release so stay tuned and/or contribute if you'd 
like to.