Support package.json configuration

[zekth]

As .madgerc is not well known around IDE, it's not detected as json formatted file. As it uses json formatting, is it thinkable to add the possibility to add madge config in the package.json ?

I can write a PR for this.

Also madge currently use rc ( https://github.com/dominictarr/rc ) so a priority between those configurations has to be determined.

[pahen]

Sure, wouldn't hurt to have support for that. I suppose adding madge config in package.json should have precedence over config files found by rc. Feel free to write a PR.