[New] add support for inspecting String/Number/Boolean objects

[ljharb]

Fixes #6.

I'm considering this a semver-minor: previously, Number and Boolean objects printed out as {} which is useless. String objects printed out as { 0: 'a', 1: 'b', 2: 'c' } for example, and now print as Object('abc'), which I consider much more useful.

There's the potential this could be semver-major due to the String change, but I don't think that really applies to this module's use case.

[brigand]

@ljharb

> var inspect = require('object-inspect')
undefined
> inspect(new Boolean(false))
'Object(true)'

[ljharb]

yay, a bug right away! thanks, will fix