Include metadata as a package object

[Nic-Chr]

Opening this to implement loading metadata into the package and to discuss.

Edit: Removed previous suggestion for the moment

[Nic-Chr]

I created a branch 'metadata' that implements this.

[Nic-Chr]

As for the strategy of including the metadata..

I think real-time is preferable but challenging but I have some ideas.

1. Create a nested list of metadata, let's call it .metadata. On package load, we read the metadata from disk and overwrite the contents of the list. I am currently implementing this approach in the metadata branch.
2. Add metadata getter functions that read the metadata on function call.
3. Attach metadata to the returned object (a la readr::spec or readr::problems- or return the metadata as an additional object

The first approach has the advantage that the user can easily view the metadata without reading anything in. The second approach is likely easier to implement.

[Nic-Chr]

A new branch 'dev/metadata' has been created and the previous branch 'metadata' is to be ignored for now.

The new code essentially loads the metadata at the point the user requests the full data and is attached as a tibble to the full data.
A helpful message is printed that highlights both the metadata and how to access the metadata.