feature: support using custom registry when retrieving package information

[regevbr]

Need to think of a way to use that registry also when using yarn install

[regevbr]

We need to have something like .npmrc where you can set registry per scope

[regevbr]

We should probably ease things up by reading .npmrc/ .yarnrc/ .yarnrc.yml from current dir

[regevbr]

need to implement something like libnpmconfig to get the config files.
Example usage in npm-check-updates