Expose the API root

[fgm]

Currently, one needs to know the desired resource, either by name or by type; and it would be useful to be able to enumerate the available resources, which are available from the raw endpoint https://pokeapi.co/api/v2/

However, in the current version pokeapi.do() is private, so cannot be used. Same for pokeapi.apiurl and pokeapi.c to take advantage of the cache.

If do was public, this would solve the issue nicely by allowing a simple call to pokeapi.Do(''), or a wrapper could be added if the desire to keep do private remains, like pokeapi.APISchema() map[string]string.