Add a flag for selecting devDependency as a default

[mikolalysenko]

The current method for selecting whether to list a package to be a devDependency vs. regular dependency is a bit ad-hoc:

https://github.com/isaacs/init-package-json/blob/master/default-input.js#L7

It would be nice if modules could specify somewhere in their package.json whether they should be installed by default as a devDependency vs. as a normal dependency. For example, I use tape a lot for the browser based test harness and it is a bit annoying having to go back and fix the dependency each time I do npm init.

As a sketch of how this could work, you could just add a field like the preferGlobal (call it preferDevelopment for example) that init-package-json checks to determine whether the dependency gets added as a normal dependency or a devDependency.

[timoxley]

Good idea, npm init jamming everything into dependencies is terribly annoying. At a minimum it'd be nice if npm didn't take things already defined as devDependencies and put them in deps.