Support loading configs from package.json/.npmrc

[LongLiveCHIEF]

I'd like to propose adding support for loading configs from npm compatible inputs, primarily the package.json file or .npmrc.

• The file override could be enhanced to read either a .json or an .npmrc
• The ENV key could be enhanced to support npm-config env vars
• A new key could be added, which loads from the config block of the local package.json file

I think this could provide added benefit to the abilities of convict:

• easier to use with CI testing tools, such as travis, which automatically take direction from the .npmrc
• would enable the usage of two convict apps on the same system, without worrying about clashing env vars
• would allow multiple config targets within a single application to do directory-recursive overrides (ex... a web app with 2 servers, a user front-end, and an admin dashboard, both can load the same config module, but receive the dynamic configuration described above)

[madarche]

@LongLiveCHIEF I find the idea interesting. What do other interested parties (@rfk, @vladikoff) think?