Introduce config file

[slawosz]

I think it would be nice to have:

gor --config gor.json

and in gor.json:

{
  'output-raw': 8000,
  'output-http': 'staging:3000'
}

[buger]

Frankly i'm skeptical about config... I want Gor to feel simple, especially if we do #46. Most likely we have to do it after some time, but i prefer to postpone this task as much as possible.

[dcarley]

I'm happy without. At least until the CLI arguments become sufficiently vast and complicated.