Interpret - as STDIN config file

[bebehei]

As proposed in #357

[tsipinakis]

While kinda a hack, isn't this already possible by giving /dev/stdin as the config file?

Edit: Actually, this isn't even a hack now that I think about it, it's intended behaviour and exactly what this PR does internally.

[bebehei]

... so what's your resolution?

[tsipinakis]

... so what's your resolution?

I'd say this is unnecessary since there's already a working solution that resolves this usecase so I'd close this but it's up to debate.

[bebehei]

The only reason, why I want to add this, is because common unix tools interpret a single dash also as STDIN (e.g.: grep, cat, etc...). When I have to give stdin as a parameter I always want to check first, if the program is able to interpret -. I actually never fall back to /dev/stdin.

[tsipinakis]

It doesn't hurt to support it I guess ^{Famous last words}