Set default for token argument in functions?

[mattpolicastro]

New to using the package and a finicky question:

RStudio flags most RGA functions with "argument 'token' is missing, with no default" when authorisation is done with environment variables and no explicit token has been set. This is fairly irrelevant, but is there a reason not to set a default argument of NULL, or something similar? It's a small ergonomics and preference question, but I'd love to hear folks' thoughts.

[artemklevtsov]

@mattpolicastro: can you provide pull request?

[mattpolicastro]

Happily! Just thought I'd ask permission before making changes. I'll start looking into implementation.