Add support for arrays

[petermorlion]

This should add support for populating arrays, i.e.

a.0.a
a.1.b
a.1.c

Will populate an array like this (structure, no values):

{
    a: [{
        a
    }, {
        b
    }, {
        c
    }
}

I believe this will fix this issue: jonschlinkert/filter-object#9

[jonschlinkert]

@petermorlion thanks for the PR and sorry for the late response. I refactored this library and will be doing a major release shortly, but I'm going to merge this anyway to acknowledge the time and effort you took to contribute. the new release also adds support for arrays.