Implement namespace functions

[ErdaradunGaztea]

Add another type of functions, wood_xxx_namespace(). They would extract both exports and imports from NAMESPACE file. The return object would have a class so that several methods could be implemented (e.g. extraction of exported names, squashing several namespaces, etc.).

Why though? Because I've got a plan for a package and it would work better to place this functionality in woodendesc.

Not needed for the release, might wait until update to plan the API better.

[ErdaradunGaztea]

• Use list structure
• Implement as.data.frame() (and as_tibble())
• Implement filters, e.g. pick_imports()

See: https://r-pkgs.org/Metadata.html#sec-namespace

The list should contain the following elements:

• import — a character vector of imported whole packages
• import_from — a data frame with two columns: source package and imported function (perhaps using a different name to avoid using an R keyword)
• export — a character vector of exported function names (variable names actually)
• S3_method — a data frame with two columns: function and class (again, work on avoiding keywords)
• perhaps additional elements for imported and exported S4 classes and methods (four elements in total)
• what about dyn_library?
• what about exclude parameter in imports?

[ErdaradunGaztea]

Note that R-universe stores _exports field in its API response, that's nice!