Add token/key parameter to set_*_repos()

[maciekbanas]

Although GitStats looks by itself for tokens it is always good to have possibility to set if by yourself. (especially if user uses different naming convention than GitStats assumes: https://r-world-devs.github.io/GitStats/articles/set_hosts.html#authorize-your-access-with-tokens).

[maciekbanas]

Done in #64