* cascade calls to:
    - user
    - repo
    - token
    - api_uri
    - skip_request
  E.g.:
  my $p = Pithub->new;
  my $u = $p->users;
  print $p->token; #undef
  print $u->token; #undef
  $p->token('123');
  print $p->token; #123
  print $u->token; #123

  Not sure though if that's a good idea.
  Probably this should only be done if the call
  was made on the root object, which isa('Pithub').

* read token from gitconfig

* add more docs, especially parameter examples

* verify mandatory parameters on POST/PATCH requests

* implement Pithub::Repos::Downloads::create