--version option

[fmang]

oshu --version is expected by most people to print the version number. Today it doesn't, because the option is not recognized.

The version number is still displayed in --help and in the man page, but it's a cheap thing to add.

[VPeruS]

gonna work by yourself? This may also include moving from getopt

[fmang]

I don't plan to move away from getopt right now.

For Windows, I consider maintaining a different binary unless I find a nice getopt alternative. We'll see.