Namespace for env keys

[monolithed]

I propose to add a prefix/namespace for the env keys

user cases

nconf.use({ prefix: 'foo_' });
nconf.set('bar', 1);
nconf.get('bar', 1); // 1
process.env.foo_bar; // 1

nconf.set('bar', 1, { prefix: 'foo_' });
process.env.foo_bar; // 1

[amtrack]

:+1:

[indexzero]

@monolithed @amtrack pull-requests welcome.

[groovecoder]

:+1:

[kkamkou]

+1