Added ability to pull multiple profiles in one request

I had to pull several hundred profiles in a row. Requesting them individually takes forever due to request overhead. Linkedin's syntax for multiple profile requests `::(id, id, id)` was not supported. I added the ability to request multiple ids by passing in an array of Linkedin Ids to the `id` option.

The request returns a `Linkedin::Mash` that has an array of `Linkedin::Mash` objects stored in the parent's `"all"` field.